M.Tech is nothing but a specialized course of B.Tech course. So, there are some restrictions to change branch in M.Tech. Master Degree in Engineering should be relevant to Bachelor Degree in Engineering.

You can somehow change your course in M.Tech. It all depends on the college you are applying for and on the subjects, you are having in your B.Tech course.

For admission in B.TECH. give JEE MAINS & JEE ADVANCED
For admission in M.TECH. give GATE

All the best!