You can purchase a new membership at all times. You can do so directly from your member's profile, either on the mobile app or on your computer. You can always choose to start now or when your current membership is completed.
You can also have more than one membership at a time. For example, if your membership you currently have doesn't allow you to register to the class, you can purchase a second membership that will give you access.
Take note that you can't renew a current membership. You can purchase your membership again or a new one.
How do I purchase a new membership from my computer?
How can I indicate that my membership starts after my current membership on my computer?
How can I purchase a membership on my mobile app?