How do I cut back on hours at work while obtaining a degree in another field?

I work full time for a company in sales. Technically, I am on a ‘career path’ and looking to veer off. I would like to go back to school for a masters and teaching certification by taking online classes so I can still work. The workload will likely require my departure from full time work. So, how do I request for fewer hours so I may obtain a degree in a different field?
FYI I am on good standing at work and love my coworkers and boss.