Upgrade to 3.90m33
Safe way go get a program called CXMB 3.1,it's a theme changer that uses .ctf theme files & there is no chance of bricking & you can store & use as many themes as you want.Just put CXMB in root of MS then go into recovery/plugins(enable the plugins & put your.ctf themes in PSP/Themes folder.Change your themes in XMB.
.ctf themes here
PSP Themes, PSP Customization, PSP XMB, PSP PTF, PSP Wallpapers, Custom PSP Themes, Custom PSP XMB
CMXB Here
http://www.consolespot.net/forums/ps...selection.html
more themes here
PSP Themes Releases - Console Spot Forums - PSP DS PS3 Xbox 360 Wii XMB
If you want to open .ctf files to change gameboots etc. use CTF Managerv1.0