How do you wear your 178 pounds? Are you muscular or have no real muscular structure? I'm 6ft too and 178 is pretty ideal, as long as your waist size is 30-32 and your body fat % is fairly lean. I would just exercise with weights, do some cardio, eat clean and make gradual gains. If you do it correctly, and long enough, you could add up to 20 lbs of good muscle. Keep your goal long term and don't cheat with steroids or the like. At your age, your body is producing the kinds of chemicals that older lifters are injecting to build muscle! Focus on your big lifts / muscle groups and don't obsess over the scale or the mirror. Check your measurements once every two weeks and you'll be surprised how far you're coming along!