There are no screws holding in the battery, only double-sided sticky tape. It's extremely strong and can take some time to remove. The best way is to slide a credit card or thin plastic object between the battery and the tape, slowly loosening it until it comes up.

I do not recommended using heat to loosen the tape! Heat can potentially increase the battery swelling and be dangerous.

There are only three sticky areas under the battery; one strip on each side and one in the middle. It's helpful if you have extra cards to insert between the battery and the tape once you pry it up — otherwise you'll have to pry each section up again after loosening.