Pretty much any sound editing software has the capability to save a file with a different bitrate.
Obviously, a more intensive application like Adobe Audition or Sony Sound Forge will give you more customizability, but even a small freebie program will probably work.
Open a project, import the clip with 12 bit audio, export the clip with 16 bit audio.
That's the easiest way to do it, and depending on your edit software may be a good way to do it. Some software is better than others (better=higher quality) when it comes to audio manipulation, so do a check of your software to see if it does a decent job.
Last update: 07:16 PM Wednesday, April 28, 2010