I AM NOT RESPONSIBLE FOR ANY DAMAGES THAT MAY CAUSE YOUR DEVICE
Your Bootloader must be unlocked and TWRP recovery installed.
-Place rom.zip and GApps on your internal SDcard
-Reboot into TWRP and make a Backup of your System (boot,system,data)
-In TWRP delete your data and cache/dalvik
-Flash rom.zip and GApps
-restart your device (first start take a few minutes)