The transmission is located on the left side of the engine, and is accessed by removing the left side cover. The transmission is a constant-mesh type, with four gears. The gears are shifted by means of a shift drum, which is located on the left side of the transmission. The shift drum is actuated by a shift linkage, which is connected to the shift lever on the left side of the handlebar.
To change second gear, the transmission would need to be disassembled and the second gear replaced.