You can get a college degree in chemistry, complete a graduate degree in perfumery, or you can work your way up through a cosmetic or perfume company. Whatever path you choose to take, you will need a combination of hard work, skill, and creativity to become a master perfumer.
How do I become a perfumer?
The best thing you can do while training in perfumery is to experience as many smells as possible and build up your vocabulary. Take notes. Buy as many samples from good reputable suppliers as possible to know what the "real thing" smells like. Take notes, smell, take notes, smell.
What training do you need to become a perfumer?
You'll likely need a degree in cosmetic science or chemistry and a lot of additional specialized training. Another option is to attend a specialized perfumer course (such as those offered by large fragrance houses), and pursue further specialized training.