hello there!

yes all the stuff related to upgradation, branch changing happens after 1st semester and reamains so for the rest of the 4 years.

yes, you can change your branch, but it is to make sure you have not freezed your branch in your first year, there will come time in DTU  first year where you willbe asked to freeze your branch if haven't freezed your branch. then, it is must you should not have any back in first year and there will be option you can change your branch. But the important thing is if seat of above preference is vacant and your jee mains marks should be good than other student who has same preferance as of yours.

Thus now if your jee mains marks are better than others and seat is vacant, you will get the above preferred branch.