The procedure to change your branch varies depending on which year you are currently in. Check the procedures below:

First year: 

• When two rounds of DTE counselling are over, some seats still remain vacant. After 4-5 days of commencement of classes, internal branch sliding is held.
• You just have to check their website regularly for notification regarding branch change. Then you have to fill a simple form. Usually, during this sliding, many IT and EC students shift to CS, EI and Civil students shift to IT and EC and so on. After all the shifts, some seats still remain vacant in EI, Civil etc. which are then filled by CLC.
• For internal branch slide, you have to go to the help centre (SGSITS) on a prescribed date and follow a simple procedure which they will tell you.

It must be noted that if you have got a seat under the tuition fee waiver (TFW) scheme then you can't change the branch you are allotted.

Second/third year: 

• In this case too, you must check their website for the Branch Transfer or College Transfer notification which comes every year around 20 July. 
• This is done to fill the remaining vacant seats of the second and third year.

Your branch change totally depends on the vacancy of seats in the branch you want to go for. Generally, some reserved category seats which are remaining vacant get filled at this time because usually all unreserved category seats are already filled after the first year. So, it all depends on your luck!