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.
Upgrade: Martha is a KidPass member. Martha subscribed to the Basic Plan - 10 credits for $49 per month - on 1/5/18. Martha loved KidPass so much that on 3/10/18, she upgraded to the Family Plan - 22 credits for $99 per month. Therefore, on 3/10/18 Martha received 22 credits and was charged $99. Her new billing cycle was changed to the 10th of each month and she was then charged $99 on 4/10/18, 5/10/18 and so on.
Downgrade: Marco is a KidPass member. Marco subscribed to the Family Plan - 22 credits for $99 per month - on 1/5/18. On 3/10/18, Marco set his account to downgrade to the Basic Plan - 10 credits for $49 per month. There was no immediate charge on 3/10/18. Marco was then billed $49 on 4/5/18 and received 10 credits. He was then charged $49 on 4/5/18, 5/5/18 and so on.