You got a buy of a lifetime there.
A: The top is easy to remove, there are two catches that look like screws.
The first one is visible in your pic above. The little chrome screw like gadget at the upper left of the top of the machine.
There is another one under the bobbin winding door. THESE ARE NOT SCREWS, to release the catch put a screwdriver in the slot, push down till it stops, and give it about a quarter to a half turn. You'll feel it release.
Then pull the top off.
The face plate is held on by a screw. Remove it and make it clean under there too. Also oil the moving parts.
B: Do not force the selector. Get some Tri-Flow and soak it. Gently work the selector till it frees up. There isn't many places that the factory will tell you to oil, but the main shaft has two or three places and anything metal to metal can use a wee bit too.
C: Pop off the narrow free arm cover and clean, clean, clean it inside. I cleaned a whole cats worth of fuzz and lint out of my wife's machine last year. The catch for that is in the bobbin compartment.
Be careful around the pattern selector levers. There are electronic control sensors under notched bar and other places as well.
Once you get it serviced you'll be amazed at what a great sewing machine that is.
Joe