Can my M visa be converted to a Z type?

Shan, it’s not easy, but it’s possible for you to change M type to work Z type. So you can have a try!
The required documents include your passport and copy of its data page, the application form with a half-length recently-taken color photo attached, valid temporary accommodation registration form, alien employment permit and invitation letter from a duly authorized unit. And then submit the application to the exit and entry administration of the local PSB to convert M type to Z type.
However, if it cannot be converted eventually, you need to go back to your home country to apply for the work Z type.

You cannot change directly from M type to a work Z type without leaving China mainland.
With the company's help, you can get official employment license and official Z type notification letter. With the 2 documents, you can go to HK to apply for a Z type. Then within 30 days of re-entry, get the final Alien Employment Permit and 1-year residence permit for work.

You need to return to your home country.

I need to know the difference between types of entry permit i:e s, m, l,z and other categories. .

Bachelor's degree is mandatory for Z visa?

Abhi, generally yes, it is mandatory.