Hello Harikesh,

After completing Diploma, You can apply for B.tech second year directly ( Lateral Entry) programme. There are many colleges offer lateral Entry programme, Each college has different criteria for the admission to programme.

Diploma students can also apply for JEE Main Entrance Exam but after qualifying JEE Main Entrance Exam, They need to apply for JEE Advance as they will be eligible to get admission in IITs only in the first year of B.tech programme.

As per the eligibility to apply for JEE Main, they should be passed AICTE or State board of technical education recognised Diploma of at least 3 years duration. You can check the complete eligibility with the given below link.

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

In case you have any other query then let me know.

Good Luck!