Not too difficult. Need the keyswitch in the #1 position.

Look at the replacement tumbler and observe the locking pawl. You're going to insert a jewelers screwdriver down the slot and lever that pawl back into the housing.

When you do that, you can rotate the outer sleeve (90 degree needlenose pliers with taped jaws are the best) until it is fully removed. If you let go of the locking pawl in the process, it will catch the sleeve on each revolution and stop it from rotating. Once the outer sleeve is removed, the tumbler comes straight out of the housing.