Hello,

Yes, you can go for BTech in computer science and engineering after completing the diploma in mechanical engineering. You can admission though the lateral entry in any engineering college.

Now come to the your next question. GUJECT is mainly entrance examination which is conduct by Gujrat state. After knowing that fact you are eligible or not I'll provide you the eligibility criteria below-

1. Candidate must be Indian in national.
2. Candidate must be domicile of Gujrat or candidate must br passed 12th examination from a school located in Gujarat or parents or candidate must be from gujrat or work in gujrat.
3. Candidates are appearing for 12th class are eligible for this examination.
4. Candidates are must be passed 12th or other equivalent examination with mathematics and physics as compulsory subjects along with chemistry/biology/computer/ any other vocational subjects.
5. Candidates must have minimum 45% marks ins 12th class.
6. Candidates age is minimum 17 years old.

All the best.