You’ve only got until tomorrow, October 15, to roll it back if you converted a traditional IRA to a Roth in 2009. Why might you want to do this? If the account lost money or you just need cash in hand, you can get back the taxes you paid on the conversion.
You’ll need to file an amended return for 2009 (Form 2010X) (PDF). Contact the IRA administrator and ask them to do what is called “recharacterize” the Roth back to an IRA.
Here’s more info on how recharcterizing works.
Act Soon to Undo a Roth Conversion [Kiplinger]