Win 10: Bitdefender Replaced By Win Defender.

Hey, i upgraded my pc to win 10 almost an hour ago, and windows decided to replace bitdefender with windows defender.


Before anyone asks, i had Bitdefender installed on my E drive so the installation of win 10 didn't touch bitdefender.


Now, i was wondering how i can disable windows defender and re-enable bitdefender? A fast answer would be greatly appreciated.