DHCP IP addresses are linked to the MAC address of the device connected to the cable modem. If you clear your current IP address, then change the MAC address of your computers NIC or your router, when you reconnect you will get a new IP
just open a command window ("run cmd") and use the "ipconfig /release" command to clear the current IP. If you are using a router, there is probably a similar command in the router's WAN menus.
This command releases your hold on your current IP, and puts it back into the pool of IPs available for new IP requests. You now have no IP address.
You can now try a few options. a) power cycle the modem, then reboot your PC (or router); b) wait an hour or so then reboot; or c) change the MAC address on your NIC or router, then reboot.