See as per the JOSAA counselling 2020-21, NTA released a willing option for candidates who want to change category from GEN-EWS to GEN which was very new for the session. So if JOSAA releases any such rules through which you can change then you can do so, else its not possible.

The major possibility is that you won't be able to change because if you enter your details in the application form then you will get a GEN EWS rank as well. So the major possibility is that you can't but lets see what happens.

To know about JOSAA counselling visit the link below:

https://engineering.careers360.com/articles/josaa-counselling

I hope this helps.