After all, this is their place of employment too. They like to work for a successful business and they love to contribute to that success. Encourage them to learn more about their work. Give encouragement to those who perform well. Reprimand those who do not perform well.
Nobody likes to work with a slacker.
The workload has to be picked up by those who are performing well. It is not fair to punish people for doing their job well to cover for those who aren't carrying their load. Always schedule time to study. You must try to improve your personal performance by learning to do your job well. As a manager, your job is to accomplish the goals of the company through people.