hi,

you may change branch or stream at second year of 3 years diploma course, You need to get a excellent score in first year . You should not have any backlog and it will be easy for you to change the branch. however stream changing options depends on the college or education board norms. some times college makes a cutoff to secure stream change option in second year.

I suggest you to consult with your faculty or person at exam section of the college to know in details.