UMD loaders can be found at psp-hacks.com . I can't help you there because I'm against piracy (and I don't have enough room for my backups) and thus, I don't use them. But I do use Devhook (the firmware launcher). Go to
www.planetpsp.org and signup (you have to do this to download, sorry. But at least its free). On there frontpage is a news artical titled "Devhook 0.43 - 2.60 Emulated FW FULL package released!" Download from the link near the bottom. In the rar file is a folder called "MS_ROOT." Copy everything
inside the folder to the root of your memory stick, and say yes to whatever crap windows tells you. Then go onto your psp and run the app Dev-hook. Hit the 'O' botton on your psp. This brings up the settins menu. Select "firmware" and select 2.6. Then select Run. Welcome back to 2.6. To get back to 1.5, just do a hard shutoff (hold the power switch up for a while).
I'm glad I could help. I try my best

. Let me know if this post helps too.
EDIT!!!!!!!!!!!!!!!
Don't go to planetpsp, go here instead:
http://fileupper.com/files/1/DEVHOOK043_FULLPACK.rar
Thanks for the tip, admin!