I recently took out the glovebox in my daughter's 1989 300TE in order to replace the A/C control fan (it is the little fan that sucks interior air through the overhead console to regulate A/C temperature).
1. Open glove compartment
2. You will see about six (I can't recall the exact number and the car is not here with me now) round, small black plugs all around the front edge of the glovebox.
3. Carefully pop the small plastic disks and you will see what looks like black screw heads under the plugs.
4. Twist the screw heads into the "open" position, pull out the plastic screws.
5. Depending on what your glovebox looks like, you may also need to remove the light assembly.
6. With a little squeeze and a little tug, the glovebox (really a felt-like lined box) slides out, revealing the content behind.
7. Installation is the reverse.
I do not have an answer for your other question.