All those thresholds are set in System Health packages which contain performance objects. The quickest way to find those packages is to do the following in the management console:
- Select Packages, System Health on the ribbon
- Click Filter and select Performance / SNMP from the drop down
- This will show you only system health packages which contain a performance object
The event alert itself includes the name of the package (Performance SQL Server in this case) and the name of the counter SQLServer:General Statistics Logins which exceeded the threshold. So for this example, expand the Performance SQL Server package, click on Performance / SNMP and finally double-click on the SQLServer:General Statistics Logins counter. You can change the threshold on the Alert tab. Save the configuration when done.
Depending on your setup you may also need to click Save & Deploy or push the configuration to the remote host(s).
I hope this explains, let us know if you have more questions.