All glass, including any type of safety glass, carries some potential of danger in handling. For safety reasons always use protective eyewear and gloves, in a well lit area when working with glass.
Removing the Vent:
The sliding vent can be removed from the frame by sliding it to the full open position, raising it up into the top frame, and pulling out at the bottom.
Disassembly 1: Measure the outside of the frame. The replacement glass (1/8" thickness) must be 1" smaller in height and width than the vent assembly.
Disassembly 2: Remove the screws from the corners of the frame. Place a block of wood against the inner side of the frame and tap against the wood, starting near a corner. Remove the side pieces in this manner.
Installing New Glass:
Replace the channel rubber on the new glass. If damaged or unusable, order replacement rubber. Install the top and bottom frame pieces first. Center them on the glass, and then tap them gently onto the glass edge until they are firmly seated. The weather-strip must be facing the same side. Install the remaining frame pieces. Screw the corners together. Before reinstalling the vent section, check that it is square using a carpenter's square. If not square, gently tap a corner of the "long" dimension until the diagonal measurements are equal.