An addition to GUEST comment:

Save the original, as noted.

If you convert to some other format, save the original unaltered conversion separately. It may provide something that can be cleaned up to better quality later, as technology advances, if the original deteriorates or is lost.

Make changes - removing hiss, blurps, farts and other noise ONLY on a second copy. You can't really remove the "noise" without throwing away part of the original, and if you add a little reverb or other effects, they may be harder to get rid of later than the original static.

John