Trying to remove a bathroom vent fan - HELP!

That whole 9" square piece the motor is mounted on comes out.

I see. But how do I get that whole piece out?

I don't see any screws or anything holding it in place.

(Sorry, I'm pretty much a DIY newbie)

Usually held in with spacer rails between the ceiling joists. Is there an attic above the fan?

The fan box was installed before the drywall was installed--the nailing ears are out of sight on either side of the box.

If you can get to it from the attic--it is very easy to remove.

If not---remove the fan -it is easy to pop out the flat metal pan with a screw driver--

Then disconnect the electric.

Push up and bend the box---slide a flat pry bar between the joist and the box and start working it loose.

-In one of those slots I see a tab that has been twisted, straighten it or them and see if that will allow it to come down.
-Feel the paper label for a screw hidden under it.
-On two of the sides of the 9" panel there may be tabs that pop into slots on the housing. Put a big screwdriver in the gap and twist it to flex the side of the housing out, allowing it to drop down.

Managed to pop it out by applying some pressure to one side (bottom part in the second picture) - there was a tab there keeping it in place.

Many thanks for all the assistance!

- H