You'll need a couple of spanner wrenches to get the lens apart. Remove the lock ring from the front of the lens and pop out the face plate, this will expose the front lens element. You can remove the front lens group, which will allow you to clean the inside of the lens. There are three screws beneath the lens element which hold on the front half of the lens housing, remove those, and then remove the small lock screw and washer-nut to expose the shutter mechanism. It's kind of difficult to reach very much because of the wires which are in the way. You can lubricate the visible linkage with fine machine oil, and hopefully this will allow the shutter to close. You can find the link which works the shutter, you'll see it move if you wind the lever and press the button. If you press the button while holding this link in place, the shutter will remain open (as long as you keep pressing on the link), which will allow you to clean the inside of the rear lens element. Keep a blower handy to blow out the dust as you put everything back together. There are schematics on Yashica Guy's site.
