Your diploma gives a basic grip of concepts in the stream. So why change? You should continue with B.tech in CSE as it would align with your diploma and reduces the confusion for your career choice, as it becomes CSE oriented.

I would say it depends on your interest and potential which branch to choose and which one should not but as you already have done diploma in CS then better to go for CS/IT branch because this is one of the most demanding branch among students from many years and it has vast scope as well but again I am suggesting kindly consider your interest and potential before you make any decision about the branch. So decide well and good luck!!!