By this I'm assuming you want to change your LAN connections IP Address.
To do so enter network and sharing center and from the left hand side click "Manage network connections"
A new window will pop up, right click on "Local Area Connection" and select properties.
Another window will open, from the list find "Internet Protocol Version 4 (TCP/IPv4)" then click Properties button.
You can now set a manual IP Address.
It might be useful to provide some info on why you need to do this, is it to solve a problem you currently have?
It's usually better to stick to getting your network address from a DHCP Server.