This 2002 Buick Century came in for a left rear power window regulator replacement. The customer was driving along and the window fell down. Pretty much a no brainer, the cable guides, on the power window regulator assembly broke.
The first step would be to remove the trim panel that covers the two attaching screws.
You can see that the retaining clips are in the center of the trim panel, in the next picture.
Again remove the two retaining screws, 10 mm heads.
Slide a tool under the front edge of the power window switch and depress the locking spring.
Lift the switch assembly up and out. Depress the latch and disconnect the wiring from the power window switch.
Using your fingers or a flat bar, plastic preferably, pry the interior door handle escutcheon plate away from the door panel.
Grip the lower edges of the door panel and pull the panel away from the door.
With the door panel removed, carefully pull the plastic moisture barrier away from the door. I try to work from the bottom up so that the top seal stays in place.
Move the window glass around so that the mounting screws are accessible.
I use suction cup clamps to hold the glass in place so that I can continue to work on the regulator assembly. You may need the helping hands of a trusted assistant.
Depress the retainer for the harness connector and remove the wiring. From this point on it is basically nuts and bolts.
The new regulator assembly should come at the correct preset level. This allows the regulator and motor assembly to first be installed into the door. Then the glass can be carefully lowered into its resting position on the regulator bracket. Install the bolts and start putting the whole thing back together.