IP addresses are unique to each computer. Every computer has their own IP address, and you cannot change it.
You have to get a different computer to have a different IP address.
Think of your house. You live at, let's say, 123 ABC street. You can't just say "now, my address is 321 ZYX street" it just doesn't work that way. If you want a different address, you get a different house.
If you want a different IP address, you get a different computer.
EDIT: Well, listen to ScottGem.
That is how it was explained to me, but he is much better at this stuff than I am.
