Hello

Yes it is  possible after 1st year .student who have exceptionally good grades are allowed to change branch .

There is two criteria for  branch changing after 1st year

1.1st year CGPA including both sem .

2. On your Jee advanced rank.

Since many student dropped iit after 1 year so in iits some vacant seats are their. So it allow students to change their branch.

Feel free to ask

Good Luck..