How can I shrink the size of my psp games?

is there a program/way to srink my psp games?? cuz i used up a lot of memory n i want to add in more games. my frens' psp was hacked.. now his psp can add in a lot of games.. up to 40.. n each originally has super big size like 1gb.. now the size of his games in his psp is read as ??? and not the usual numerical values.. can someone teach me how??