There is no easy to remove old paint – just scrape, scrape scrape. You are asking about mold – do you actually mean thick mold, or just mildew discoloration on the paint? If the latter is the case, I have a formula for mildew removal.
2 tablespoons dish detergent – Dawn, etc
2/3 cup Trisodium Phosphate (TSP)
1 quart bleach
3 quarts water
Mix solution in a pump up garden sprayer and apply to the offending area. Let it sit for a few minutes then hose off with clean water. When thoroughly dry, prep and paint.