You dont have to downgrade it m8

If You have Grand Theft Auto: LCS:

1.Goto http://www.fanjita.org
2.DownLoad the Eboot Loader from the Eboot Loader Page
3.Follow the Read Me you get with it to install it on your psp.
4.Go back to http://www.fanjita.org and goto the Working Eboots (GTA) Page.
5.Download the Emulators you want, Homers RIN is a good GameBoy Emulator. Dgen is a good Sega Genesis Emulator.
6.Place it in the Game Directory on your Psp. (PSP->GAME)
7.Download your roms, and place the in PSP->Game->Roms, You cant put them in any folder, but this is easiest to remember.
8.Load up Grand Theft Auto.
9.Goto Load Game, choose Eboot Loader from the selection.
10.Select which emulator you would like, then play your roms!

PS- Might be a good idea to backup your GTA file. Just incase the Eboot Loader overwrites your file. This is very rare though.

This Tutorial should work for 2.60 Firmware and below!