GRRR - I am repairing an old pair of diacompe break levers. These are the ones where the break cables run along the bars. I can not figure out how to find the screw that will loosen them from the bars.
I tried the dia-compe web page - it is kaput - only an 800 number
Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
Like zona said, pull the lever as if you are brakeing. Look in the crack that is formed at the top when you pull the brake lever. It may be helpful to use a flashlight the first time. Straight inside that crack, behind the brake cable if you have one installed, you'll see a allen bolt or some kind of screw. Loosen that and the brake lever will slide down the bar.
If those are the levers you have, you'll see there's a small slot in the front of the lever. That's for accessing the clamp screw. If you depress the lever, it actually brings the cable and stop forward and down, hiding the bolt head.
If you've got older-style non-aero levers (which it sounds like you don't) that look like the one in this photo: http://www.zweknu.org/uploads/noahsbike004.jpg then depressing the lever will reveal it, but you may have to disconnect the cable (which can be done from the cable head in the lever unlike the other style) in order to get at the bolt.