In some cases lessons that you book may not be suited for your specific level. Whether you have under or overestimated how good you are changing lessons is easy enough providing that you let your instructor know right away.
If you do feel like your lessons aren't helping, normally instructors will take the initiative and look to move you into a more appropriate level group. If your instructor doesn't mention anything to you and you still feel like lessons are not helping just let them know as soon as possible so that you can join another group.
Whilst we do make every effort to give accurate descriptions of the different level of lessons sometimes lesson content can vary depending on how competent the group is on the whole.