Diploma

If you are looking for a college, you should take certain things in account.
Caste
State in which you are comfortable
Cut-off range of colleges
Best of luck!

Since you have already completed your undergrad it is advisable to go for higher studies like a Masters rather than pursue a Bachelors course again. However, if you want to change your line of study, you could opt for a B.Sc. You could also try getting some counselling to get a more accurate picture.

Yes, you can as in India you need to give NATA entrance exam and then after clearing the same you can take direct admission in B.Arch architectural colleges.
But remember that not all colleges accept NATA scores, so you need to choose the college which accepts NATA score with 3-year Diploma score.

Hello Bansal,
The following are the top diploma engineering colleges in Mumbai:
1. A. C. Patil college of Engineering, Mumbai
2. Academic of Engineering and Management, Mumbai
3. Atharva Educational trust, Mumbai
4. Bhavan's college, Mumbai
5. Cambridge College, Mumbai
6. St. Xavier's Technical Institute, Mumbai
7. Government polytechnic college, Mumbai
8. K.J Somaya Polytechnic College, Mumbai
9. Premlila Vithaldas Polytechnic, Mumbai
10. NMIMS University, Mumbai

Hi Ramesh,
You can join some of the popular colleges mentioned below to pursue a course in front office management:
Amity University
RIMT University
Maharshi Dayanand University
SRM Institute of Hotel Management (SRMIHM)
For more information on colleges offering courses on front office management, please follow the link:
https://www.shiksha.com/hospitality-travel/hotel-hospitality-management/colleges/diploma-front-office-management-courses-delhi-ncr