Downgrade help Plz!!

I'm new to this forum and have been reading extensively about downgrading my PSP. I don't want to screw it up by doing it wrong. I've downloaded everything I need I think, but am still unsure if I need to downgrade to 1.5 before I upgrade back to 303 oec or 310 OE. You guys are obviously a lot more comfortable with this stuff than I am. My current version is 303. I can't see any numbers inside the UMD tray and the number at the bottom of my PSP is 1001 I've tried directly upgrading to 310 eoa but my PSP won't run any of the PBP files. I'm lost (and very new to this) Any help you might be able to give me would be greatly appreciated
Thanks

Your 3.03?

To do the 3.03 downgrade you need a copy of grand theft auto:liberty city stories unpatched.

if your on 3.03 as trivium said you need GTA LCS unpatched in order to downgrade, if you have a copy then your laughing and the downgrade is easy.

Ok Thanks guys. Looks like I'll have to head out and pick it up. I might be back asking more stupid questions

I finally found GTA LCS. it says "Greatest hits" on the front cover. I think I bought the wrong version because nothing happens when I follow the downgrade instructions. just keep getting "corrupt data" message. I've re- downloaded the files, but nothing is happening.
Can anyone help this old guy out please?

re-read the instructions maybe?