How do you change plumbing from a two handle faucet to a one handle faucet?

Just change it. There are still hot and cold connections underneath and all kitchen faucets fit the same holes in the sink.

ANS 2 - Very easy to fit another faucet, all you need is basic handyman skills, a plumbers faucet wrench (sometimes) a medium crescent wench and a 9/16 flat wrench. Takes about 30 minutes.