Online Course. The most convenient way to become a personal trainer is to take an online course and then take their certification exam. These courses will teach you everything you need to know about becoming a personal trainer and will do an excellent job at preparing you for their exam.n average training program takes around 6 months to complete. Many gyms and fitness clubs are now accepting a College or University degree in a fitness related field instead of requiring you to become certified. These take from two years for a diploma to over four for a bachelors degree.