compression question

ok so im expirimenting with making a mod uninstaller for a game of mine but the file size is almost 50 mb which is a pain to download if i distribut it i have about 60.1mb of data in archives for it but need a way to reduce file size anymore any ideas

notes:
the archives are cab's so i can use a cmd line interface to extract them automaticly(better ideas are welcome)

theres a uninstaller doing the same thing im trying to but the file size is only 39.6mb but i cant figure out how they got it that small

i ripped apart their installer and found it contained 137mb of data or so in its installer package once fully extracted any ideas how i can match this iv gotton about the same size down to 60 and that took several archives and compressions