In January session I got 81 percentile. I entered my category as general. But can I make it general ews on April session for jee mains. then for cutoffs my which percentile will be calculated. 81 percentile or which I will be getting in April...

Avinash, you can change your category during April session. But since you have applied as a general category candidate in January session, your rank will be given as general category candidate in April as well, then during the counseling, you will be given a choice to select your category and rank will change.
For marks, the best of two will be considered. If you get more marks in April, than that will be considered final. If not, then January session is final.

Hope this helps!