Use the "wipe" button from main menu and "factory reset" (wipes data/cache). On the checkboxes, I wouldn't change anything from the defaults.
Sent from my XT894 using Tapatalk 2
what's the difference between 'factory reset' and wiping 'system', 'cache' and 'dalvik'? I'd have thought the latter would clear the slot, but when I re-installed the ROM I still had my app data. I assume that a 'factory reset' would only apply to the active slot, but I'm afraid to try ...