Don’t use chlorine bleach or any other chlorine-based mildew cleaner. It can kill you and the mildew. If you have a mildew problem bigger than ten square feet, you’ll want to call in a professional.
To clean mildew, you’ll need some distilled white vinegar, an empty spray bottle, baking soda, gloves, and an aggressively abrasive sponge. Vinegar will kill mildew, germs and bacteria and is very cheap. Cleaning mildew with vinegar will also do away with that bad mildew odor. The baking soda and sponges help remove mildew stains. Lastly, you’ll need a mask.
Fill the empty spray bottle with the white vinegar and don’t dilute. Liberally spray all the affected areas. After spraying the mildew, let it sit for a couple of hours to allow the vinegar to penetrate and kill the mildew.