From the sidebar, select Settings, then click Account.

The Settings window will then pop-up with your account information displayed. If you currently are subscribed to a HootSuite Pro plan, a green "Modify or Upgrade Plan" button will appear on the right side of the window. Click this button to be directed to your Billing screen.

Once at the Billing screen, select the amount of reports you would like to purchase. Keep in mind that by purchasing one report, you are actually purchasing 50 points since this is what one reports typically costs. Actual reports may vary in price. When finished, click the Save Changes button.