First, turn the drone over, so it is right side up, and facing away from you. Now, use a metal spudger to pry open the rear end of the case. Be careful not to pull too far up, as there is still a cable which is connecting the two pieces.

Slide the spudger down the length of each side, undoing all the clips along the way, stop 1-2 cm before the ending of the battery cradle.