hi,

see in most of the university rules students of engineering course like b.tech or b.e may change their branch after first years study, since the first year syllabus is same to all the department, so it would easier for the student to grasp the subjects in second year studies what ever branch he/ she may allocate to. now the change of department solely depends on your first year academic score , you must secure a very high score of above 9 point cgpa to change the department, also there would be quite competition among students and highest scorer gets the priority.

another options is internal sliding , after getting admission in college you may apply for branch change, however it also depends on whether the particular department has seat vacant for more candidates.

hope it would help.