Cleaning lenses on projection screen HDTVs?



I have a Hitachi 55" RP HDTV that's about 3 years old. My HDTV pictures
(cable) are not as sharp as I think they should be, and I'm wondering if the
lenses are dust covered.

Is it necessary to have the lenses cleaned of dust, etc., every once in a
while?

Also, does anyone know where I can buy a service manual for it?
.