In the Planning Search panel, you can view your alerts. It's from here that you can edit the name and/or the area (using the pencil) or delete them (using the trash bin).
Click on the alert to start a new search with the same filters or add/change the terms. From there you can create a new alert.
You can also view your alerts by clicking "Dashboard", then "Planning" and "Toggle Alerts". You can turn an alert on and off from here.