How do I revert from using the new March 2013 Facebook version and get back to using the old Facebook?
What "old Facebook?" 2012? 2011? 2007? Facebook constantly changes their user interface, adding and removing features as they go along.
It has never been a part of their design philosophy to diverge interfaces for people to use older versions (except in a select few instances where Facebook users could "preview" new features). That consistency amongst all users has long been a part of their branding, and it isn't all bad. For example, it doesn't do any good when troubleshooting to have to play a guessing game of what sort of layout the user is viewing Facebook from. We can see that sort of inconsistency when comparing Facebook viewed on a PC to a (perhaps watered-down) mobile Facebook app.
You will, perhaps unfortunately for yourself, simply have to get used to the new interface if you wish to continue using Facebook. I would also like to take this moment to advise you against searching for services online to change the interface, as they are very likely scams.