It's always best to backup your microSD to a folder called backup on your PC before upgrading to a new firmware version.

Then format your microSD with the Panasonic SD Formatter and use these options :
FORMAT TYPE - FULL (Erase ON)
FORMAT SIZE ADJUSTMENT - ON

Then extract the files from new firmware and copy/replace the following to your microSD :
_PATCH folder
_system_ folder
Games folder
TTMenu folder
_DS_MENU.DAT
_DS_MENU.INI
_DS_MENU.SYS
DEFAULT.nds
r4dldi.dat

Copy usrcheat.dat to TTMenu folder

