Mildew thrives in damp environments and is very difficult to remove. Use a grout brush with hot water to brush away as much as you can before applying a solution. Next, soak the shower walls with distilled white vinegar since the vinegar kills over 80 different types of viruses, it breaks down mildew, and kills mold. Vinegar is also non-toxic, the smell will dissipate within 3 hours or less. Also, use a cloth and wrap around the spout and any handles. Spray the vinegar over the cloth and let it sit.
After about 20-30 minutes, use a cloth to wipe down all areas. To prevent further mold build-up and to cut back on maintenance, always dry the shower walls after each use or spray the shower walls atleast once or twice a week.