Usually when you need to remove moss from the roof, there are three steps to go through: 
1. Kill it. You can do this by applying chemical moss killer, or by some natural means. It’s rumored that applying baking soda to moss can help kill it. Another way is to hire a reputable roofing company to go through the whole process.
2. Remove it. This can be done very carefully with a pressure washer. You must make sure the water doesn’t actually get under the shingles. This part is actually best done by a roofer as it’s delicate.
3. Prevent it. There are items like zinc strips, which can help prevent moss encroachment.
Here’s to a clean, moss-free roof!