I've never uninstalled but I think this will do it... I really haven't messed with any of the PS3 disk stuff--
Start up the PS3-- from the main menu,
Go to Game--
Select Game Data Utility
Select GTA IV-- push the triangle button - if you select info it shows the amount on the hard drive-- mine shows 3.357 GB
Above the info is a an option to delete-- I don't know for sure if that deletes all the IV data-- the info screen shows my initial install date-- and has version 1.01- so I don't know if that deletes the "patch" data or not...
I did not see the Metal Gear Solid 4 online beta game in there (which I do have installed and it is completely on the hard drive) so there probably is another way to access your hard drive files--
anyone???
I would try and verify this before you try this... I accept no responsibilty if this messes up your game further...
I do wish you luck.
//edit//
for the MGS4 if I go into that game from the game menu- and select triangle there is an option there to delete it...
Sorry can't help more-- I've only had my PS3 for about 6 weeks and most of the time it is on I'm playing
