I recently hit a deer and messed up my 850 pretty badly. The glass on both lights is shattered. I recently purchased a new piece of glass for the headlight but do not know how to install it. Any help is appreciated.

 

If the case isn't cracked you just need to remove the "C" clips around the perimeter of the lens. These clips hold the lens against the gasket against the housing.
Just be gentle and use a flat blade screwdriver under the clamp and pry up. Be prepared for it to pop loose.

 

and the marker light just needs to be replaced.