It would help if we knew the rough age of the bike, and whether it has flat bars or drop bars.
On my Dawes with drop bar road levers, you loosen the levers on the bars by disconnecting the brake cable and pulling on the lever until the lever is touching the bar. The screw to loosen the lever is now revealed in the gap between the hoods/main body and the actual brake lever. (If that makes any sense at all..)
Pat has pretty much covered Flat bar levers.