Early 13" and 19" GK cabinets can't be upgraded. If you have a 17" or 19" Panda cabinet then all you need is the 044MPU board and motherboard like ANIslots said. You'll also need a flash memory card with the game software to plug into the MPU board. I'd suggest getting Super Stars poker. It has full versions of both Wolf Run, Coyote Moon, and single/multi-hand poker games as well.
If you don't have an upper button deck you can still play with out it, you'd just have to use the touchscreen to select the number of lines to play.