First you need to know that the screws are thinner then average flat head and will strip the screw of you try to force it. So look around and see if you have one that fits properly. ( my father had one.)
There is a tiny screw in the knob on the side of the machine. (the knob with the different stitches shown all around. All black knob)
Remove the screw, be careful because it is tiny! And then remove any of the screws on the four sides of the plate. After you remove those screws the plate should slide right out over the knob that turns the needle. (no need to unscrew that one) that will give you a clear view of the cam stack. Now just rotate the wheel that move the needle and it rotates the cam stack. You should be able to see of anything is wrong.
Good luck!