There are two screw's on that hold on the black cap on the left side of the saw (left if you are holding from behind) Remove those two screw's and you will have a good view of the brushes, and the armature. Check the brushes, and give everything a good blow out with compressed air. That's all you really need to do.
I would recommend Dewalt's new 7 1/4" circ blade. It currently out-preforms anything currently on the market, and the 24t is priced at $9.97, Lowe's has them as a buy one get one free which makes it even better!
ToolsInAction did a review on the blade
here.