the adhesive is 3 narrow pieces of double sided tape. You can carefully peel it off the old battery and reuse it. I don't see where it's absolutely necessary though. The battery isn't going to move around after the phone is put back together.

Step 4, there are also 2 T shaped tabs on the sides locking the mid frame plate. Above them you can see an angled hole where you can insert a paper clip to push them out and up to unlock them.