In the allotment process you have an option 'Accept or Freeze'. Here select freeze option and search if there is any available seat in Signal processing Stream, If there is chance you can upgrade to Signal processing stream otherwise you have to take only Communication Engineering only because it's decisive. So, I always wish to get your dream branch in Engineering All the Best. 

Hello,
By the reference of your question I will suggest you that if you are not fully assure than you didn't go for upgrade still you want the same than you can make a try. But before trying something make yourself confident.

Hope it helps!

IIT Guwahati (IITG)

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