Diploma

Hi,
There are many best institution where you can opt for Diploma in construction management. Some are mentioned below:
1. Toi Ohomai Institute of Technology, Rotorua, New Zealand
2. Whitireia New Zealand, Wellington, New Zealand
3. Unitec Institute of Technology, Auckland, New Zealand
4. Manukau Institu

Yes, you can change your stream. It is possible.

Yes, it is beneficial as you can launch your own range of clothes in the fashion field. You can also be a fashion designer and work under a fashion designer or you can start your own fashion boutique.
All the best.

Hi,
To study in Canada, the minimum band should be 6, but you should check with the universities in Canada. Some may offer you admission.

Hi,
As you are doing Diploma in mechanical, you have plenty of scope other than studying BE. If you are not interested in studying BE then it would better enough that you don't go for it.
As you have done Diploma, you can go for a job because, nowadays, there are more opportunities for the one who ha