Loosen (removal is not necessary) the two screws that hold the black plastic pen carriage cover in place. Slide the cover forward to remove it. Remove the 4 screws that hold the plastic carriage track rail cover. That is the piece on top the spans the full length of the track rail. You should be able to access all the screws for tightening.....unless the rollers are shot or need tightening but I don't see how they would need to be tightened. Those screws usually have a thread-lock added when assembled. If they are in fact loose.....I can't help you there as I have never needed to get that far into mine.