If you want to change your plan, go to "Account" menu in the upper right-hand corner and click "Plan" tab in the pop-up window. Then click the big yellow button named... "Change plan".
You'll see another pop-up with dropdown menu. Choose the plan (see our plans and pricing page here) that you want to switch to and click "Yes".
When you upgrade to a higher plan, the change will be immediate and you will be charged the difference between your current plan price and the new plan price until the end of your current billing cycle.
When you downgrade, the change will become effective with your next billing period. Please note that you will need to delete excess social profiles and users according to your new plan limits before the current billing cycle ends. Otherwise, your account will not be downgraded.