Answer: To pursue M. Tech in Computer Science & Engineering, you must qualify in GATE (Graduate Aptitude Test in Engineering) examination. You are eligible to appear for GATE only if you have studied Mathematics as a full paper in your Bachelor degree. If you have pursued your MCA through distance education mode, you are eligible to sit for GATE if you satisfy the other criteria, i.e., having Mathematics at the Bachelor degree level. You can appear for GATE in the year in which you are about to complete your MCA requirements. Generally, you have to complete the MCA program by June of the year in which you are seeking admission to M. Tech course.
Getting into IITs will be difficult for you even if you have a high score in GATE. IIT Mumbai does not take MCA candidates unless they have B. Sc. with Physics and Mathematics. It is the same with IIT Kharagpur, IIT Delhi, and IIT Kanpur. IIT Chennai may take you.
Some other institutes offering M. Tech in Computer Science & Engineering