Hello ,

After diploma in mechanical engineering you can go for engineering by lateral entry that mean after diploma you can get admission in college in b.tech second year.

And some top colleges which provides lateral entry are :

Anna university

Jadavpur University

Thapar University

PSG College of technology

Amity University

Delhi technological University

BMS College of engineering

Kalinga institute of industrial technology

PES university

Sikkim Manipal institute of technology

You can go for these colleges by giving there entrance exam .

There are few entrance exam which you can give for admission in these colleges or other colleges by lateral entry  :-

Haryana LEET

Kerala LET

Ptu -leet

UKSEE

JELET

All the best!!