The first step is to click on Manage at the bottom left corner of SalesScreen.
A menu will pop up, where you can proceed to click on Events under the Gamification headline:
Once on the Events management page, you will get an overview of all the events which have been created and are either active or inactive. To edit an event, simply click on it.
You will be presented with the event creation wizard, identical to the one used to create an event. Edit the fields that you deem necessary and click the Save button: