You sure can! You can change your membership plan right in your Account Settings. From there, you’ll see an option to 'Adjust your Membership plan' under the Membership Details section.
If you’re switching to a plan with fewer credits, your plan change will occur at the start of your upcoming cycle. If you’re upgrading to a plan with more credits, your billing cycle resets, your card is charged the full price of your new plan, and the credits are applied to your account immediately.