you will need a pair of needle nose pliers, and a small allen wrench or a large paper clip.
that's it.
put the key in, turn it to the second click, put the paper clip in the hole above the key and press until you feel the button release, then unscrew the collar with the needle nose pliers, then pop out the tumbler, and put the new one back in, put the collar back on and remove the paper clip.
that's it in a nutshell.
I asked the dealer how much to do it when I picked up my tumbler, and they quoted me 300.00

I did it myself.

I did ecaxtly as above. Used thin brazing wire, filed both ends 60 degrees inside, turned to second click, inserted the wire in both holes till it bottomed in but can not unscrew the the collar even with the needle nose plier. I put the needle nose plier ends in the collar holes and tried to unscrew it but will not budge. Am I not doing it right?