The foot should come up without much force. If it feels stuck, apply more heat and try again.

Insert the point of a spudger under an end of the foot.

Push the spudger underneath the foot and lift until you can grip it with your fingers.

Peel the foot up and remove it.

Repeat the previous two steps to remove the remaining feet.

If you're just replacing the battery, you only need to remove the feet along the top edge.