Backup your µSD to a Backup folder on your PC BEFORE upgrading to a new Kernel

Format your µSD with the Panasonic SD Formatter 3.1
Use these options :
FORMAT TYPE - FULL (OverWrite)
FORMAT SIZE ADJUSTMENT - ON

DUAL BOOTING :
Download the latest Kernel from your carts website and extract to root of your µSD.
Extract these files from R4i-SDHC YSMenu folder and copy to root of your µSD :

Games folder
TTMenu folder
TTMenu.dat
YSMenu.nds

Boot your carts Kernel, then load YSMenu.nds.