Yes you can definitely change or upgrade your stream in 2nd year but your CGPA plays a major role in branch upgradation.Many Engineering colleges allows or provides you with the opportunity of getting a branch of your choice in 2nd year cause in 1st year all your subjects are common but in 2nd year your core engineering subjects that are related to your branch come into light.
I myself got my branch upgraded from Information Technology (IT) to Computer Science Engineering (CSE) in the first year on the basis of my good GPA in 1st year.
The cut-offs depends on the branch or stream and it varies accordingly for Example CSE has the highest cutoff followed by IT,ECE, Mechanical. Majority of students want to upgrade to CSE because of benefits and perks that they visualize after graduating with it. CSE (Computer Science & Engineering) is also a hot topic in market these days and majority of graduates wants to pursue it be it Toppers from IIT,NIT or private Colleges like Manipal University or VIT.
Moreover getting a branch of your choice gives you self satisfaction and it is also an important decision as you have to deal with the branch for your complete life.