How To Downgrade: The Nube Chronicles

My PSP is version 2.5, and I'm trying to get it downgraded to 1.5, if possible. Does anybody have an idea? Also, side note: I ported over my copy of FFIII, and for some reason, it keeps getting stuck at this one part, I'm using SNES TYL and I can't figure out a way to get it to move along...any ideas? Because I've got some serious time behind these characters.
Thx.

there is no downgrader for 2.01 + but if you want to play homebrew you can get GTA Liberty City Stories.

I figured as much, I read a few posts on it and kinda figured it out. Can you help with the stuck game file though? I find it uber annoying.