Yes, you can cancel your membership at any time as a free or monthly paid member. If you are a yearly member, you can cancel at any point before your one-year renewal.
All you need to do is log in to your account, head over to your subscription and cancel. You are not locked in for 3, 6, or 9 months if you choose the month-to-month option.
If you know when you want to cancel, make sure you cancel before your next billing cycle to avoid being charged that upcoming month.