Once you have popped the two halves of the case apart, you'll see the circuit board inside. It simply pops out. Inserting a finger into the battery compartment makes this very easy.

After the circuit board is removed, you MAY see a white plastic retainer holding the transponder in place. Sorry, I don't have a picture of the retainer. It just slides out, so no worries there.

Once the retainer is removed, you can see the transponder.