-For the 2.71-
http://www.pspbrew.com/forum/viewtopic.php?t=6810 , If it doesn't have a TA-082 board, then just skip step 4.
-For the 2.81-
http://www.pspbrew.com/forum/viewtopic.php?t=7034 , Same as above statement^^, just upgrade from 2.81 to 3.03, and you will need GTA:LCS an unpatched version which means it has copywrite 2005 on it and update 2.00 when you put the UMD in your psp.
-For your own psp, 1.50 isn't a custom firmware, and neither is 2.71 unless you have 2.71SE, or whatever version it is. You must be using devhook or something. So just upgrade to either 3.03OE-C or 3.40OE-A. Those are the 2 most common custom firmwares people use. You can go to the download section to download the custom firmwares. And you shouldn't brick if you just follow the instructions included in the readme's. I mean really, follow the instructions and the comments I made then you should have about the same chance of bricking as you do when you upgrade to a Official Sony firmware.
Correct me if im wrong, but didn't I already answer your question in my previous posts?? Sheese.