How to replace garage door window
 

I'm trying to replace a window in an aluminum, sectional garage door
(Overhead Door Comapny).
The window seems to be held in place with 4 U-shaped plastic strips
with grooves on the inside. I'm not sure if they are also glued or
not. So, before I pull too hard and do more damage, what's the proper
procedure to replace a window mounted this way?