Ok real quick question.

[Dude]

So I want to help fix some sheets, but I want to use some of the current sheets as a guide.  How would I write the "Arrangement by " part? Should I add both names or how does that work?

[Winter]

If you changed enough of the sheet to make it nearly new, just use your name. If you feel that the previous arranger did enough that their name deserves to be on it still, leave theirs on.

[MaestroUGC]

Or, include on the opposite side of the page: "Edited by ___". That would technically be the most correct in score production.

[Winter]

I haven't seen any of our sheets use that format, but you are welcome to do what Maestro said.

[DonValentino]

If you changed enough of the sheet to make it nearly new, just use your name. If you feel that the previous arranger did enough that their name deserves to be on it still, leave theirs on.

I did that with the "Fairy Fountain" from Zelda OoS and OoA. Just left "Leftie"s name on it, even the original arrangement lacked of key signature, octaves and repeats... 

[Winter]

And that was your choice. But you could put your name on it.