Dear Bapu
If  you  have taken admission through AIEEE in NIT's  then it is possible there are two ways.
 
 1.Branch sliding
 2.Branch change
1. Branch  sliding
 
After your  admission any NIT in the  month of September-December  if any of  the  seat in any branch remain vacant due to some reason then it is filled by   the respective candidate of that state or UT on the basis of your  AIEEE rank. Here  you have a good chance to change your branch once more  but it totally depends  upon
 
 (a) No. of seat vacant 
 (b)Your AIEEE rank
 if your branch is not changed till  now then don't worry  you will have another chance to change your branch and  this time it  will be totally depend upon you and your academic performance   throughout first year. This is a golden chance for you.
 
 2.Branch change: 
  This happens at the end of  second semester to give a chance of  meritorious student to change their branch  but rules are different from  institute to institute. Like
 
 (a) Minimum no of marks/CGPA(combined grand performance index)required in  your first year
 (b) Max. no of seat available for branch change.
 
 Here  it totally depends upon your academic  performance  so be ready for this and work hard throughout year to catch this   opportunity.
 
 Even now if your branch is not  changed due to some reason  then don't be disappointed. If You want to change  the branch for job  opportunity reason only, then don't worry because now a days  software  companies are allowing each branch for recruitment and you can be a   software engineer .It does not matter from which discipline you are. So  enjoy  your studies and best of luck