Purchased a new 2500 tow mirror from Ebay a couple weeks ago, and tonight I tried to get my broken lens off to show how to do it. Here are some photos with a little description.
2500 Tow Mirror with Defrost and power.
Mirror housing with the mounting tabs... notice the tabs pointing to the mounting base of the housing.
The Mirror, with the "female" end of the tabs facing to the right.
The "male" end of the tabs that the mirror clips into on the housing.
See the trick is, and yes the mirror was already broke, when you want to take the mirror out, disconnect the defrost connectors and then you have to push the mirror over in the direction of the mounting studs on the mirror housing. In this case, the RH Mirror, you push to the left.
To reinstall the mirror, place on the housing tabs and push the mirror over to the end of the housing. In this case, the RH Mirror, you push to the right.