How to catch bigger bass on Clark's hill lake

Hey my name is justin guin and I was wondering if you could help me out and give me some tips on bass fishing. I'm in the military and currently deployed over seas right now but I have been fishing for almost 15 years now on Clark's hill lake. I have also just invested in a new nitro z20 and me and my friend back home fish alot of tournaments on Clark's hill lake but we always come up short. I was wondering if you could explain somehow to catch a 15-20 In bag on that lake. I know it's possible because people do it every tournament. Me and my buddy have no problem catching small one(***) Ilbs just can't seem to break over that 15-20 Ilb mark for a five fish limit. So if you don't mind please give some advise on the situation