There must be some screws you are missing on the bottom.
I would just use a very soft damp cloth to clean it and then a soft cloth to remove any streaks. Unfortunately it is made of plastic not glass, it doesn't scratch that easily but it will scratch.
So don't use any real cleaning agents, maybe some normal soap at most - like Ivory or dove, etc. But I'd try with just a damp cloth first.
The manual used to be available for download for free somewhere, I have it but not sure if it could be emailed. It is 8 meg.