so long as your careful with all the bits, its simple. The case comes with all the screws for the motherboard and such (and bolts for the fans).
just remeber to keep the bits on a soft surface that isnt wet or anything (foam or polystyrere is best) and as a precaution 'ground' yourself before you pick up a different part each time (just touch the nearest metal radiator or something).
also, if you want (and if you end up doing this) when you take the heatsink and fan off the processor you can put some new thermal paste on to see if that helps at all.
But theres nothing complaicated about stripping down and re-assembling it, although connecting the power switch and LED status lights can be a bit fiddly, course if you get stuck you can ask here