There is no such thing as an "orange plastic lamp". Neither is there "3 screws at the top". I wish people wouldn't give out duff info.
1. Remove the coals.
2. Most (but not all) Dimplex fires have two screws either side in the front of the grate assembly. Remove them and lift away the entire grate/fuel effect assembly.
You will now have access to the lamps. Some models require a flame effect rod to be detached if the fire is not the ribbon type.
Lee, March 2009