How did you try to change the IP address?
Try this. I am assuming you are using cable modem and router.
If you are connecting through the router. Try changing the Mac Address of the router (most routers provides a way to change it). Then turn off your router and modem for few minutes and turn back those again.
Verify your IP by going to http://whatismyipaddress.com/
If it did not work, try releasing and renewing the IP address at your router. If every time your router getting same IP then directly connect your PC to the modem and see if it gets different IP.
If you are directly connected to the internet, do the similar things at your laptop / PC.
The idea here, is you could get different IPs for different Mac addresses (Network Interface Card Addresses). If they all did not work, keep your router and modem turned off for several hours. Then at next start, it might get a new address from your ISP.