To download the Resident Evil 4 PSP ROM .torrent file, you'll need to use a torrent client, such as BitTorrent or uTorrent. Here are the general steps:

The most exciting reality behind these searches is the existence of dedicated fan projects. Brilliant independent developers have spent years building "demakes" of RE4 specifically to run on PSP custom firmware (CFW).

Some torrents include a PC emulator (e.g., Dolphin for GameCube/Wii) with an RE4 ROM for a different platform—but the actual game still won’t run on a PSP.