Click ->System Preferences -> Network.
Choose the interface (wireless or ethernet).
Click the Advanced button.
Click the TCP/IP tab.
Choose DHCP for automatic IP address, or "Manually" to pick it yourself.
If Manually, enter your IP address, your subnet mask, and your gateway address, along with the proper DNS info. Usually, best to leave all this at DHCP, and let it take care of that for you.
It was already set to DHCP, but if I picked Manually how do I find the IP addres subnet mask etc? How will this change anything if I put in the same IP as before?
Oh, sorry I haven't replied yet.
The main reason why I need another IP is to get back onto a forum I was incorrectly banned from. It's a long story, but I really need to get on the forums now but for some reason I was banned, and it banned my IP.
So changing my IP should let me get onto the site again, correct?