Removing acrylic caulk
Caulk mildew stains can be very difficult to clean, especially if these stains are below the caulk. In this case it’s not worth even trying to clean the stains. You should try and remove the caulk, but this is a job that takes time.
For scrapping the caulk you can use a utility knife or a razor blade, but these can scratch the surfaces.
To remove the rest of the caulk you will need to use some products, depending on the type of the caulk. If the caulk is non-acrylic, then you can put a wet carpet on the surface. Let it sit for several days. The caulk will swell and then it can be peeled off. If the caulk is acrylic, you ca remove it with most isopropyl alcohol.
Silicone caulk is the most difficult to remove. It can resist almost all solvents. Use the information provided bu the manufacturer.
The best way to deal with mildew is to prevent it from growing. For example, you can paint the walls with a glossier paint, use mildew additives, install a bathroom vent.
Applying the new caulk
First of all you will need to cut the tip of the tube at an angle. Now you can apply the caulk. For water-based caulk you can use water to clean and smooth the caulk bed. In case of silicone caulk you will need lacquer thinner. This is a flammable substance so pay extra attention.
Apply two feet at a time, but work fast. Wipe the excess caulk to prevent it from hardening and sticking to the surface.
Try and buy more expensive caulk because these have the best resistance to mildew.
For cleaning mildew you can use water and bleach: one part bleach and 4 parts water. Add some laundry detergent and then apply the solution on the affected areas.