Use the manual for more details:

Warning: Turn off the fireplace, and allow time for the unit to cool before proceeding.

Caution: The ceramic glass is very fragile, and should be handled with care.

Warning: Double glass fireplace should NEVER be operated without the external glass

Step 1 – Remove lower trim by releasing the screws. The number of screws will depend on fireplace size.

Step 2 – Attach glass suction cups to the glass and release the glass upper frame. The upper frame is attached with 10mm spring bolts.

The top glass trim gap will open once bolt is released and will allow the glass to be removed. Upper trim will stay attached and only open to be able to remove external glass.

Step 3 – Tilt the bottom of the window frame and rest it in the gap between the external frame and glass holder.

Step 4- Tilt the top of the window frame and lift out to clear the top edge of the unit. Place the window frame in a safe place to avoid damage.

Repeat the steps above in reverse order to install the external glass back.