What will happen to my kidney disease if i get in really good shape?

Yes: It depends on type and severity of kidney disease. Regular exercise, good, healthy diet and avoidance of smoking, other illicit drugs helps and improves many chronic health conditions like hypertension, diabetes and high cholesterol. Hypertension and diabetes are leading causes of kidney disease in the world. Adopting healthy lifestyle definitely improves the chronic illnesses.

Depends on disease: Hard to answer. It depends on the type and severity of the kidney disease. Controlling blood pressure, salt intake, and urinary tract infections is the best way to maintain kidney function.