Hello VIN,
Once you get the activation key from cisco on the UR bundle, you just need to upload it into the PIX , using a command "activation-key xxxxxx"
Just refer to the following URL to active your license keys to the PIX.
http://www.cisco.com/warp/public/110/upgrade.shtml#upgradeactivation
Hope this helps.. all the best... rate replies if found useful...
Raj