Diploma

Yes, you can get admission for aeronautical engineering after completing Diploma in mechanical engineering.
But I would suggest you to continue in mechanical engineering because it has huge scope in near future and you can also go in aeronautical field after that.

Hello,
You are actually already abroad. So you are in a better position to answer your query. Universities abroad normally understand and accept 10+2 students for an undergraduate course. But diplomas are not equated with 10+2 and hence I feel it would be difficult for you to go anywhere for graduation with diploma. But perhaps in Singapore itself you can bid for admission for B.Tech.

Hello Sandeep,
UGC is involved in approving degree level and above courses. AICTE approves degree level professional courses. Diploma is below graduation. You should look for government approved polytechnic.

Hi Venkat,
I hope your preparation for JEE Mains is going awesome. You will be glad to know that you are eligible for appearing in JEE Mains exam after completion your Diploma. Check yourself by visiting the link given below:
https://scoop.eduncle.com/jee-mains-eligibility-criteria
As per the eligibility criteria for JEE Mains, those who have completed there Diploma with a minimum aggregate of 75% are eligible for appearing in JEE Mains exam. Those who are in the last year of their Diploma are also eligible for appearing in the JEE Mains 2018 exam.
So, be happy and crack this exam.
All the best.

Drop this plan if you want to get good jobs and placement then go for BBA in HR and then MBA in HR so as to make your skills superior and fetch out a good salary package.
Good luck.