Changing bulbs on my electric fire?

I have a Dimplex Adagio electricl fire, model no. ADG20. I need to change the bulbs that operate the Optiflame effect and have contacted Dimplex as I cannot see how to do this. They told me that you simply lift off the fuel-effect plastic cover and replace the bulbs which are under it. However, I cannot lift it off. Please don't tell me it's easy, because three friends have tried too, and none of us can do it. Their manual is not helpful; it states "remove coals and lift off plastic fuel-effect cover" but it doesn't tell you how. Please help!