Yeah, you need to take off the overhead light panel to get the rearview mirror in.
Take off the overheadlight lens and then there are two bolts you'll need to remove in the light well. Remove those as well as two clips in the front of the light assembly (closest to the windshield) then you should be able to remove the assembly by sliding it towards the windshield and down. There's an electrical connector you may have to unplug as well after you remove the overhead light assembly.
There are then 3 screws holding the rearview mirror in place.. so just screw it back in and put everything back and there ya go. Don't forget to make sure the little rubber damper piece is still attached to the windshield to hold the mirror steady. Otherwise whenever you drive the mirror will shake which is really annoying..
Good luck!