You are now doing diploma in ECE so you are not eligible for B.Tech course in CSE or any other branches.

You can apply B.Tech course in Electronics and Communication Engineering subject only.

So you have no chance to do B.tech degree in CSE.

By the way, I want to mention another clarification for you.,

Yeah there are chances that the candidate can change the stream from one to another (If you entered in B.Tech after 12th only ). This could be possible when the candidate is in 1st year.