Go to Configure > Tools > Automations and Collection Extensions > Collection Extensions and click the name of the Collection Extension to edit.
Once in the Collection Extension, make sure you have editing enabled by clicking on the lock icon at the top-right part of the screen and then press the Edit button.
Then, in the Edit Collection Extension view, you can change its name, select another action to perform, provide arguments for the action, select if you want to run it as the user or the system, or select the runtime limit. On the right-hand side, you'll be able to see the documentation for the selected action:
Once you are done editing, press the Save Collection Extensions button to save your changes.