WAV is the format audio software actually wants: uncompressed 16-bit PCM that loads into Audacity, Reaper, Audition or any CD authoring tool without a conversion prompt. If your WMA files are heading for restoration work — declicking an old recording, levelling a set of voice memos, splicing tapes together — convert to WAV first and stay lossless through the edit.
Files are large, around 10 MB per minute of stereo, which is the normal cost of an uncompressed working format. Export to MP3 once the editing is done.
Editing without stacking losses
Every lossy encode discards a little more detail, and the artefacts compound when you edit and re-save repeatedly. Decoding once to WAV and working there means only a single lossy step ever occurs — the original WMA encode — and everything after it is exact. That matters most for old recordings you're trying to improve rather than simply move.
It bears repeating that WAV can't undo the original compression. A 64 kbps WMA becomes a very large file that still sounds like a 64 kbps recording. What you gain is a clean surface to work on.