Diploma Students are eligible to apply for JEE Main Entrance Exam but they can not get admission on JEE Main Score, To Qualify JEE Main is the process to be eligible for JEE Advance Entrance Exam as they will be eligible to apply for IITs only into  B.tech first year. 

To apply for JEE Main Entrance Exam, You should have AICTE or State board of technical education recognised Diploma of at least 3 years duration. For further information Click Here

If you wish to take admission direct into second year of B.tech programme, There are many colleges offer the programme, The admission criteria varies college to colleges.

Good Luck!