@asimzaeem Which oil are you currently using? And why you wanna use 20w-50? Won't it be too thick?
I think, 5w-30 would serve the purpose best. Do not switch to thick oil, unless / until your car engine is weak, it's consuming / burning oil.
Regarding complete maintenance of your car, you may visit AutoReforms garage. It's at Ali Nawaz Chowk, Rawal Road, Rawalpindi. You can get your car fully maintained from there, with complete peace of mind and satisfaction. Their charges are reasonable and they have proper tools and knowledge of cars.