You have two options for performing this; neither one is particularly straightforward: Option #1 is using cloning software to copy the Windows partition to an image on an external drive, then using another computer (depending on whether you used an OS X program or a Windows program to do the clone job) to restore it. Option #2 is simply reinstalling Windows, formatting the whole disk in the process, without Boot Camp's help.
Beware, though - if Apple releases firmware updates for your Mac, you will be unable to install them.