Only your School Certifying Official can increase the number of credits you are enrolled in. The correct thing to do in this case is to verify your enrollment at the lower credits and training time and contact your School Certifying Official to correct the VA records.
NOTE: Schools are not required to report credit hours over and above what is considered "full time" at their school. So, if VA considers 12 credit hours as "full time" and you are taking 15, the school may only report 12. This will not affect your payment rate.
If you have further questions about your account, please contact VA using the "Ask a Question" tab on our web site (in the Questions and Answers section) or by calling 888-GIBILL-1 (888-442-4551).