There is a catch. The 3.03 downgrader requires an unpatched version of GTA:LCS. If you don't have it, then do not upgrade to 3.03. Instead, open your UMD tray and look at the top right corner of your PSP and check to see if it says 'TA-083'; if it doesn't say that, then you are safe. If you do have the unpatched GTA:LCS, then Google the term '3.03 firmware download'; that will most likely find you the 3.03 update!
Find the appropriate downgrader at: N00bz!
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Dark~AleX - PSP Developer