Assuming you have a Custom Firmware (CFW) installed on your PSP (such as PRO-C or LME Infinity), here is how to acquire and install the game.
To avoid the infamous "ring rope glitch" (ropes disappearing): Wwe 12 Psp Download
The most common search is for a free WWE 12 PSP download. Let’s address the elephant in the room. Assuming you have a Custom Firmware (CFW) installed