The caps are held on with 4 small plastic bar shape tabs, 2 on each side of the cover.
The plastic is getting very old and brittle, so be gentle. (I broke one of mine on the first time removing them. )
You can use a thin knife tip or anything thin enough to get in the crack and pop it off.
Do it from the INNER side so if you scratch it, it won't show.

Each cap is SPECIFIC to the location, so there's 4 different ones, and they're marked on the inside as to position.