What is the best & easiest way to remove mildew from bathroom roof (im a short person) & i live in Australia?

A flat microfibre mop should reach unless you have very high ceilings and are very short. You could use it with water only or with a bit of bleach to kill any remaining mildew.

Is it the ceiling in the interior of your bathroom or is it outside?

Bathroom ceiling: Wear old clothes, goggles or something to protect your eyes: Wring-out a sponge mop dipped in a bucket with water/bleach solution. Mop the ceiling. You'll need to use a rag and get on a ladder to get the corners and other areas you aren't able to reach with the mop though.

Use a foam mop and a bucket of water with bleach in it. "Wash" the ceiling with the mop.

When it dries, use the same mop with a cleanser to remove the dead spores.

well i mean i know how to get it off the roof in america, but australia...man i got no idea.

bleach