Staff Name

I am writing several general percussion parts, I named them Perc 1, Perc 2, etc. These parts have several different instruments. When I changed the instrument on count one of the piece, it changed the name of the part to that instrument. For example, on the score it no longer says "Part 1" it says "Anvil" because that is the first instrument on that part. How do I change it back to "Part 1"?