Not risky at all as long as you don't force anything and make sure you don't take any heat sinks off.
For what it's worth I use a balloon pump to blow the dust off the fans in my PC. If you've got one (or maybe a bicycle tyre pump) it might be worth taking a shot at blowing it through from the air intake vent. See what (if anything) comes out.
edit: Switch it off first of course.This might help?
You don't want to do all of it, figure out which steps apply.