Instructions
Download ISO Change 1.2 at http://psp.dashhacks.com/downloads/iso-change-v12.
Unzip the installation folder. Transfer the files iso_change.prx and GAME.txt to your Sony PSP. Put the files in the "seplugins" folder. If you do not have a "seplugins" folder already, create one.
Hold down the "Note" button, the left trigger and the right trigger simultaneously. This will launch the main menu.
Use the left and right directional keys to cycle through the available UMD files. To make navigating your UMDs easier, make sure that they have clear, distinct file names.
Press the "O" button to run the highlighted UMD. To cancel your selection and return to the previous screen, press the "X" button.