S6 Edge plus coming from Vietnam already rooted?

Hello folks,

I just received my EDGE Plus and when I hit the Power, Home and volume down button it has taken me to the Root Custom ROM option with Odin pre-installed..anyone ever had an issue with that before?:confused:

Easiest way to upgrade to marshmallow when already rooted?

Easiest way to update to marshmallow when i'm already rooted? Will it delete all my ****? Do I need to make a backup? Thx in advance.

Won't enable USB debugging (already unlocked bootloader)

Ok so first time I unlocked the bootloader the process was straight forward and everything went great.

Now that twrp was released with the modded boot image, now I can't get my phone to be recognized.

When I type in adb devices it shows nothing. I tried turning off on usb debugging and tried MTP, PTP, Charging etc. Tried factory reset also and restarting laptop.

Any more suggestions? I never had a problem waiting for usb debugging allow option to click yes but I'm stuck right now