I'm not familiar with Linksys's router menus, but look through it and there should be a field where you can type in or clone your MAC address. A MAC address looks like 00-00-00-00-00-00, where the 0s are a value from 0 to 9 and A to F.
To get to your router menu, you go to your web browser and type in 192.168.x.1 (x is a number) and login. If you don't know the exact address, go to Start > Run > "cmd" > "ipconfig"
Look for your Default Gateway. That should be the address you will be typing into your web browser to enter the menu.