Your IP address is assigned to you by your ISP. If you have a router, that too can assign each of your computers plugged into the router an IP address by using DHCP.
You can unplug the power chord to your cable modem, and router if you have one, and generally leave it unplugged for at least 5 minutes then plug it all back on again.
Sometimes it works best if you leave the power unplugged for overnight. You then will be assigned a different IP address. Regardless though, that IP address can still be identified by your ISP as belonging to you.
In short, follow these steps:
1. Get to a command prompt. (START, run, cmd).
2. Type "ipconfig /release" (without the quotes).
3. Shut down computer and router if you have one.
4. Turn off computer.
5. Turn off all ethernet hubs/switches.
6. Turn off cable/DSL modem.
7. Leave off overnight.
8. Turn everything back on.
I hope this helps.
Good Luck!