Yes, you can do diploma course in Mechanical Engineering.

Those candidates who have passed matriculation/10th with Mathematics, Physical Science & English from Central or State Board recognized by Govt are eligible for Diploma entrance exam.

Your age should be below 21 years.

Source:http://entrance-exam.net/forum/general-discussion/commerce-student-can-i-do-diploma-mechanical-engineering-2002195.html#ixzz5Y849O5Io.

If you are Graduate then y u want to change to engineering when there is more option in commerce than other field.

The regular post-graduate courses

1) Masters in Commerce
2) Masters in Business Administration (MBA)
3) CA/CS/ICWA
4) Certified Bank Manager Programme
5) Diploma in Banking & Services (DBFS)
6) Certified Financial Planners
7) Certificate Course in Project Finance
8) CRISIL Certified Analyst Programme (CCAP)
9) Certified Management Accountant (CMA)
10) Certified Public Accounting (CPA)
11) Association of Chartered Certified Accountants (ACCA)

Thanks,
Azim Shaikh

Dear Vishnu

Vishnu unfortunately a Commerce graduate will not be eligible for any engineering courses or diploma because inorder to do that you need to have Maths , Physics and Chemistry till your Class 12th. So unfortunately commerce aspirants will not have all these subjects so commerce aspirant won't be eligible for the engineering and diploma Courses related with the engineering.

All the best