Returning a lease machine is easy.
If you're rolling it over to another lease (new equipment from same vendor) they will handle everything for you.
If you're not getting another machine, you just need to contact the leasing company. They will want to charge you some amount to have the machine crated up and shipped back to them. However, here's the secret: THEY DON'T WANT THE MACHINE BACK. What are they going to do with it? So, if you want to keep the machine, they will give you a buyout price. You negotiate that price with a counter offer - remember, they really don't want it back, so, you really have more negotiating leverage than you think. Now, compare the final negotiated price to what it would have cost you to crate the machine up and send it back, and, 9 times out of 10, you'll find that you came out on the good side of the deal.