To start with, your function should have a parameter for the parent, too (unless your tree has pointers to parents, which it sounds like it doesn't).
With that change, it should be easier for you to figure the rest out. But how you call that function becomes important.
Note: I'm assuming this is homework, so I don't want to provide a comprehensive answer.
Also, for the logic of what to do with the nodes after one is removed (how to relink them), try drawing some diagrams.