Top cover of the VFO comes off but some versions have a couple of screws on the front of the VFO. If so you can remove them slowly using a pair of needle nose pliers or quickly using a short bit (if screw) with a ratcheting wrench or just the wrench for the hex head screws. I have some really thin ones but these will probably work OK:
http://www.harborfreight.com/4-piece-sae-offset-ratcheting-wrench-set-68834.htmlBut before you go into the VFO do you have the later model (or modified) that adds the 12AU7 keyer circuit? If so check the keyer tube and make sure that the pot is adjusted before digging into the VFO.