The Distribution Tab on the Dashboard will give you access to your Distribution administration section.
Underneath the Step 1 header you'll be shown how many email distributions you have left and when your current subscription will renew. Your allowance will reset upon your renewal date, but if you use up your allowance before then you can easily top up.
To do this, you can either contact your Account Manager, the Support team or click the Get More button. This will provide three different email bundles. The instructions are shown in the screenshot below.
You will then receive an email from the Support team confirming your selection before processing it.