On this page you can select a security level to edit. Click on the profile you want to edit:
Hi - High security (firewall inspects both incoming and outgoing traffic)
Lo - Lower security (firewall inspects incoming traffic, but allows through all outgoing traffic)
AC - User defined security level

You are recommended to edit AC only. The other profiles should not be changed.

Active Profile - To change security profile select it from the list and press Change.
To permanently select the profile (so that the profile is automatically selected each time the unit is powered on) press Save Permanently on the Administration page.

Resource Allocation

Flows
The firewall creates a "flow" for each data stream to stateful inspect. The more flows the more data streams can be open through the firewall at the same time. But having too many flows reduce performance and memory available for other tasks.

In use - Number of flows used by the firewall right now.
Peak - Highest amount of flows ever used by the firewall since last power-on.
Total - Maximum amount of flows available to the firewall. Values 500 - 8000 accepted. Recommended values are 4000 for home users, and 7000 for small offices with many PCs behind the firewall.
If the current or peak amount of flows approaches the amount total available then you should increase the "Total" value, press "Apply" and then save permanently at the top of the page. Then restart the unit by powering it off and then on again to get the new value activated.

Read more online:
Security Settings