Cover the floor in front of the fireplace in case you drop something.  Release the clips or screws at the top of the glass and remove it from the fireplace.

You can use:

     -Paper Towel or Rags

     -Water

     -Water & Vinegar Solution

     -Gas Fireplace Cleaner

     -CLR

You cannot use:

     -Windex

Windex contains ammonia which can react with the sulphur in the natural gas resulting in discoloured glass. 

Ensure a tight seal when replacing the glass to prevent harmful fumes from entering your living area.