Hello,
In any of the NITs or IITs you can take admission in first year in any branch and you can upgrade your branch to CSE.
In order to upgrade your branch to CSE you need to maintain a decent CGPA above 9 and an excellent academic performance in first year.
Getting a decent CGPA doesn't guarantee your up gradation to CSE, it also depends on the number of seats available in the branch.
Hope you got the answer.
All the best.