For sewing cotton fabrics I have found that sharp or microtex needles are best, universal needles aren't good for that. Its not hard to put a new needle in, just make sure that you put it in correctly for your particular machine.
I have quite a few old Singers and some of them have the needle flat either to the left or right and of course they all thread differently. :roll: When I go back to using my modern machines I have make sure that I put the new needle in right.(bad news if I didn't)
Take the throat plate off and clean all the lint out;
and the bobbin area and oil it if your machine requires it.
You'll be suprised at how much better your machine sews.