Meaning, it's not been updated to 6.0, is it possible to install a "fresh" copy of 5.1.1?
The shift trick in iTunes or something?
If it is not jailbroken you can do an "erase all contents and settings" from the settings/general/reset section of the phone, which is not entirely like a fresh restore in iTunes, but may do the trick depending on what you need.
If jailbroken, do not attempt this !
I assume you are jailbroken because of the section you are posting in, but just in case you aren't...