Account sharing. - If you're account sharing and DO get banned for it (very unlikely) say that you play at a relatives house anyway this may help, depends if you're on router.
On the command prompt (go on run and type cmd) type this: "ipconfig/release" without quotation marks.
Actually forget my lousy explanation this is courtesy of the best site:
www.whatismyipaddress.com:
Windows (second option) - Computer connected directly to the modem
Get to a command prompt. (START, run, cmd).
Type "ipconfig /release" (without the quotes).
Shut down computer.
Turn off computer.
Turn off all ethernet hubs/switches.
Turn off cable/DSL modem.
Leave off overnight.
Turn everything back on.
Network with Router
Log into the router's admin console. (Often
http://192.168.1.1/)
Release the IP address. (Method varies by router manufacturer)
Turn off router, ethernet hubs/switches, and the cable/DSL modem.
Leave off overnight.
Turn everything back on.
If you are using a cable/DSL modem and a router, you may wish to connect your computer directly to the cable/DSL modem. Please note that this could significantly impact your system security. This allows your ISP's DHCP to issue you a new (hopefully changed) IP address based of the (hardware) MAC address of your computer's ethernet card.
If all the above has not worked to change your IP address and you have a router, check and see if there is a "Clone MAC Address" option. Using it should change your IP address, however, you'll only be able to do it once (in most cases).
This has always helped me, there is also a program to change IP but it will make you appear from Russia :$