I requested my manager to change my grade from BPS To IT and he is agreed on that and someone told me to get grade change BPO3 to BPO4???

If you are preparing for Wings 2 then don't go for BPO3 to C1. Because in C1 it will change to Wings 1 and it will difficult to clear if you are non technical background.

Disadvantage from BPO to CC grade is your offer letter won't change and Cab service will be stopped If you are availing it.

I have been taking regular follow ups and things seems positive so far

All managers agree to BPS-IT conversion/Promotion

But the question is how soon?