Usually, 10w-30, 10w-40, 15w-40 and 20w-50 are suggested and recommended for Mehran's engine.
If your vehicle is currently working absolutely fine on a particular engine oil grade (let's say 20w-50), I would sincerely suggest to continue using it and not fiddle with it. You may just change the brand.
Regarding brands; Shell, Total, Caltex / Havoline, and even PSO, KIXX, ZIC, are some of the reputed brands, which are abundantly available locally. I would suggest to choose between these, instead of going for expensive, fancy, imported engine oils.
I hope, it helps and guides. Thank you.