To change plan, choose Account > Plan
This screen shows the available plan options, your current plans shows up as 'Current'
To change your plan, choose the right plan for you and click Change Plan
Confirm your payment options and click Subscribe
Please note: Subscription fees are pro-rated. This means that if you upgrade your plan midway through the billing cycle, you will be charged the increased subscription fee only for the remaining days of the month. If you downgrade your plan midway through the billing cycle, you will be credited for the difference between what you've already paid and the lower charge, for the remaining days of the month. That credit will then be deducted from your next months subscription payment.