B.Tech

Yes, you can join B.Tech after completing Diploma in Mechanical Engineering. As you have completed Diploma in Mechanical Engineering, so you can join B.Tech in Mechanical Engineering, Aeronautical Engineering and Automobile Engineering only. You can get admission in Engineering colleges through late

I would recommend you to go for B.Tech after HSC as you will be having a lot of entrance exam options and college choices to go for, but if you join B.Tech after Diploma then there is only one examination for lateral entry (LEET) and the college choices will also be less.

To get this minute detail, I would recommend you to get in touch with the current students through social media or in person.

Kindly follow the link below and check the admission information :
https://www.shiksha.com/b-tech/course/b-tech-in-computer-science-and-engineering-klu-college-of-engineering-guntur-177409

College change or university change after the first year is completely dependent on the college and university norms, some universities allow it and some won't plus you need to have good scores in the first year to apply for the same. For further details contact the college authorities.

The college takes admission on the basis of MHT-CET and JEE Mains scores, direct admission is only possible through management quota and management quota admission/fee cost is not advertised openly by any of the colleges/universities across India as being a paid seat it totally depends on the discre

Parul,
Yes, it would be a better option as compared to Pune University, for details check out the reviews below :
https://www.shiksha.com/university/parul-university-vadodara-30821/reviews

You can check the reviews for both the colleges below:
https://www.shiksha.com/college/l-j-institute-of-engineering-and-technology-l-j-i-e-t-sarkhej-ahmedabad-38282/reviews
https://www.shiksha.com/university/indus-university-iu-ahmedabad-31348/reviews