gragra,
I don't think Billy is here any more. At least I haven't seen him post in a very long time.
A couple pics would help us with our on-line diagnosis.
There are maybe three or four methods to remove presser feet, and most of them use a thumb screw either from the left side or the rear. Always turn the screws counter clockwise to loosen them.
However the machines that use the top clamp feet have a big nut on the presser foot shaft right above the foot. Turn that nut counter clockwise to loosen it. If needed wrap it in a piece of leather and gently encourage it with a pair of pliers.
Also WD-40 is not a good penetrating oil or lubricant. You'd be better off with Tri-Flow oil. It really does what the others claim to do. Make sure you clean the WD-40 out of your machine and re-oil it with sewing machine oil or Tri-Flow. You'll be happy you did.
Tri-Flow can be had at Sew-Classic {
http://www.shop.sew-classic.com/ } and some bicycle shops.
Joe