The transmitter comes apart easily. Once open, remove the components and discard. Next remove the old car key. Use a small nail or paper clip to remove the lock pin that holds it in place. I took the key I wanted to replace it with and cut it down with a hacksaw blade to a rough shape. Then I put it on my bench grinder until it was the same shape as the original VW key. I used a Dremel tool and the hacksaw put a small notch in just the right place to accept the lock pin. Insert the new key and lock it in place with the pin. This took about 10 minutes of trial-and-error...it's really not too hard.