As MunkeyBoy states, it really depends on your goals. If your goal is endurance than high reps with lower weights is appropriate, however, if muscle development and strength are the goals then you should decrease the reps to say, 10 or 12 but increase the weights by at least ten percent. Additionally , check with a trainer or some other knowledgeable source to vary the workout. The same muscle group can be worked in different manners to produce different results. Example; the common bicep curl will produce more muscle mass if done from a bench sitting position rather than standing since the chance for assistance (especially at higher weights) from other muscle groups is reduced. Be sure to use appropriate vitamin and mineral supplements, and rest, rest, rest... (you are breathing correctly during the workout, aren't you?)