Are you saying you don't have an Administrator account on the system? None of the accounts listed in User Accounts say "Administrator" under them? Well, that may be another issue as only an Administrator can change permissions and do other things. When you start the computer, do you get a Welcome screen and choose your username and login or do you hit CTRL-ALT-DEL and enter your username and password to login or do you just login automatically - going directly to your desktop with no login at all? Also, please go to Control Panel / User Accounts / Manage other user accounts and take a screenshot of that page and attach it to your next reply.
To take the screenshot, just click the PRTSCR button on the keyboard. Then go to Start / All Programs / Accessories / Paint and open Paint and click on Edit and then click Paste to copy the image. Then click File and Save As and name it whatever you want but be sure to change the filetype to .jpg and save it wherever you choose but remember where that is. Then when posting here, click Go Advanced and click on Manage Attachments then click one of the Browse buttons and find that .jpg file you saved, click OK to select it and then click Upload to add it to the post.
You're saying that permissions for both of the folders say your username has full rights. In the special permission section, does it say anything about inheriting access rights (to the right)? The limitation may still be imposed above the folders we're looking at. I assume you've checked <username> and AppData for your user account (you should
not have had full rights to AppData unless you did this before - it's possible even Administrators don't have full rights at first and need to grant them to themselves so being the same a Administrators may not be enough unless they both include full rights - and being the only user makes no difference at all in terms of access permissions (except to perhaps complicate things if that user isn't an Administrator)).
It's now time to check the Users folder itself and not only add your username with Full Rights in both places but also take ownership as well. I'm not sure why this is being so difficult because it worked fine when I did it on my system - but then I was an Administrator when I did it and to be honest I'm not sure to which folder I applied the permissions and ownership (knowing me, I jumped right to the top the first time to be sure inheritance wouldn't give me a problem).
First, here's additional information on taking ownership (and make sure you select to do so for all sub-directories and files at the same time) - the prior post already provides details on permissions:
To fix this problem with the folders, take ownership of the folders or the drive (as an administrator) and give yourself full rights. Right click the folder/drive, click on properties, go to the security tab and click on Advanced and then click on the Owner tab. Click edit and then click the name of the person you want to give ownership to (you may need to add it if it isn't there - or it may be yourself). If you want it to apply to sub-folders and files within that folder/drive, then check the box for replace owner on sub-containers and objects and click OK. Back out and now there's a new owner for the folders/drive and files who can change permissions as needed. Here's more information on taking ownership of a file or folder: http://www.vistax64.com/tutorials/67717-take-ownership-file.html. To add take ownership to the right click menu (which will make it faster to get in once it is set up), check out the following article: Context Menu - Take Ownership.
Now, about the Administrator problem. We may need to activate the Built-in Administrator account to add a normal Administrator account or two to the system and to make the permission and ownership changes (or we can use the created Administrator accounts to do that if you prefer, but since you'd already be logged in as an Administrator it might be easier to just kill two birds with one stone). I'll have a better idea once I see all the available user accounts from the screenshot. Here's the procedure: http://www.vistax64.com/tutorials/67567-administrator-account.html. We may also need to revise how you login so we can access an Administrator account, but I'll know more about that once you tell me the procedure you're using now.
This is being much more painful than it should, but we'll get it done eventually and get you access to that folder and ultimately to the file you need to edit. It's almost hard to believe that simple task was the original purpose of all of this (and we haven't yet confirmed that's the right file yet either). But on the positive side, you are learning a great deal more about permissions and ownership and administrator accounts, so the time isn't wasted. I learn something new every day here and it's one of the reasons I keep doing it (surpassed only by being able to help people with questions and problems) and believe learning is both enjoyable and useful.
I sincerely hope this helps. This is one of the times I regret no longer having GoToPC available so I could see your screen and guide you directly and get it resolved a whole lot faster - but alas we don't have that tool here (it's $60/month per person!) and I discontinued my business subscription when I went part-time as a cost I could do without. But even if this doesn't work (and I'll need details of what you did and how and why it failed at any step), we WILL find a way to get it done somehow.
Good luck!