Hi

You will have to enquire about this in both the colleges. Mithibai allows cancellation but before that make sure you got confirmation from somaiya that they are taking you in ( if your name was in merit list and the admission date is not over) and you need documents too that you have submitted in mithibai for admission that you will get only after cancellation. Once you are sure of a seat in somaiya should you proceed for the cancellation process in mithibai. Enquire with them about the process and other details they have the final say.

The link for application is given below

https://mithibai.ac.in/Junior%20College/M__553

Hope this helps!