The world is always changing, so if it's been twenty years since you attended college there are probably many different viewpoints in your field of study that weren't around when you were in school. Don't be afraid to challenge the things that you were taught in college. Ask your employer or coworkers about their opinions about different viewpoints in your field. Challenging the thoughts that you developed in college, will help keep your education fresh in your mind and will also help you to expand upon the things you have learned.
If you are a working professional who doesn't have the time to devote to learning a new skill, consider attending a conference or seminar for work. Your employer will more than likely be thrilled that you want to attend a conference or seminar and will gladly give you some time off to learn some new things. Continuing your education through conferences and seminars is a great way to make sure that you stay up-to-date with your education.
Reading is a great way to improve your education levels and keep your past education fresh in your mind. Choose to read books that involve the area of specification that your studies took in college if you want to refresh your memory about your past education. Even reading the newspaper every morning will help keep your education fresh. When you read, you are exposed to new ideas and these new ideas force you to challenge the information you learned throughout your education.
Many working adults with families are taking the leap and going back to school despite their busy schedules. If you can afford to go back to college and earn a higher degree or a completely new degree, you should do it. There is no better way to keep your education current than to continue learning throughout your life. If you don't want to get a new degree, consider enrolling in a shorter program, like a professional certification program or just taking one or two classes at your local community college.