At the bottom of the clutch cable you will find a nut. This will either need to be tightened or loosened. You will need to adjust it until there is less than 1/4 inch of play between the part that attaches the lever to the handlebars and clutch lever.
There are two places you can adjust the clutch. First you can loosen or tighten the screw on the clutch lever, second you can loosen or tighten the nut on the engine where the clutch cable attaches. You should only have to pull the clutch about 1/2-1 inch to release.