Can't delete categories

When I select the default categories the remove button is greyed out, so I have way more categories than I need with no way of deleting them.

Yeah, looks like you can’t delete default categories, but you can rename them and maybe replace some you created.

I only need two categories, and I couldn’t get them to work anyway, only new categories work

Yes, you are stuck with 4 extra categories.  How do they not work?