How to download iso/cso games with 5.50 prometheus-4 for my psp?

Every time i go to download a game and put the file into the "ISO" folder on my memory stick it successfully goes on but then when i go to the main menu of my psp there is no game there. Am i like suppose to change the settings on the VSH menu or something? I really need help so if anyone could help me that would be great.