Flashing a BIOS is relatively simple, however it is not without risk.
Generally speaking there are two main ways of doing it.
One is downloading and putting the new BIOS on a USB flash drive, floppy disc or burnt to a CD and updating through the BIOS itself. This method is the most preferable, as there is 'less risk'.
The other method is to flash the BIOS from within Windows itself, usually via an downloaded BIOS *.exe .
However while it's a 'simpler' process, it has a much higher risk of causing a 'bad flash'. A bad flash can render some motherboards inoperable.
If you wouldn't mind, could you please download CPU-Z and post a screenshot of the 'mainboard' and tab:
CPUID
Example:
To post a screenshot:
A Preferred Method of Uploading/Posting Screen Shots - Windows 7 Forums
(It's our sister site, but the method is the same)
I used there ram on it on and pc booted up fine swapped memory around in the slots still no joy!
By this, do you mean the PC worked fine with only the new ram installed?
If so the supplier was correct in that it is compatible with your board, but not necessarily compatible with your existing modules. The good news is that you may not have to flash your BIOS.
Now for the annoying part which involves more ram swapping
In CPU-Z could you also post a screenshot of the 'SPD' tab of both your old ram only and your new ram only. This will determine if the CAS Latency timings I mentioned earlier match or not.
Example:
If they do not match, then there may be some further things to try. If they
do match then it's back to the drawing board.
One last possibility is that depending on your board, it may have a maximum limit of 2GB and if that is the case, then unfortunately there is nothing that can be done
(* Before swapping your ram modules, I'd like to check the specs of your mobo first (mainboard screenshot) - I should have added this step first, but I thought of it last

)