If you do not have yet installed a Cognos server or if you do not want to allow all users to access to Metrics within Communities you might want to hide the "Metrics" link which is visible to every user by default.
To do this open the Websphere Integrated Solution Console and click to
Applications -> Websphere Enterprise Applications -> Communities -> Security role to user/group mapping
Select the role "community-metrics-run" which is set to "All Authenticated in Application's Realm" by default and set it to "None" (or whatever user or group you like).
Synchronize all nodes and restart the Community application.
Now the link should no longer be visible to every user.