Remove the screw at the top left of the glass pane

Remove the screw at the bottom left of the glass pane

Then gently lift the 2 tabs of the screws you just removed, and slide the whole glass pane by about 1/4inch (5 mm) to the left

(Note: Avoid any dust inside the scanner unit.)

You can stop here if you're not interested in the printer part, or put back the glass pane and go on.