How do I go about officially breaking ties with an old church?

I've been an atheist for about a year and a half now, but I have not officially broken ties with my last congregation. I haven't actually attended in a long time as being a full-time student has allowed me a good reason to be reclusive. However, I'm the type who really prefers to have closure. I would like to go back once and say my goodbyes. Even though I'm not terribly close to most of the people there, I still respect them as individuals and my reasons for becoming an atheist really didn't have anything to do with them. Any advice for saying goodbye and minimizing drama?