Hello,
Bsc and btech are different degrees. So, you need to join btech from the first year if you want. As it depends on the course nad college you are interested in. Sometimes there are also entrance exams for btech programme so you need to appear for one you can't directly go to btech from bsc.
Hope it helps.
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile