Basically it's the same as this tutorial here: http://www.sb-innovation.de/showthre...?threadid=9761
but in this case you have a router and of course a dynamic ip.

1. Go to your router's config page

Most routers default gateway is 192.168.1.1, 192.168.1.2, or 192.168.1.0 but you can find out quickly by typing ipconfig in cmd prompt. Then again you should know it if you set up the router in the first place.

2. Depending on the brand and/or firmware of your router you will have different options

a. Find the option to release DHCP, which will tell the router to signal your ISP to release the IP address it has currently assigned.
b. Now, usually under internet settings, go and change your mac address for the router. You should have an option to clone mac address of your computer so if you haven't done that already then click clone. This step is probably the most important because otherwise when you go to renew DHCP it will give you back the same ip.

3. Click Renew DHCP. If you can't or if it doesn't do anything, unplug your modem to power cycle it and plug it back in. When it reconnects you should have a new ip address.