All events will be transferred automatically to use the default price list's prices and products when the sales end date passes.
1: Go to products and prices https://upgrd.io/settings/products
2: Create a new price list or make a copy from an existing price list.
3: Rename the price list something that you will recognize, for example My default Price list.
4: Set it as Default price list.
You will see now that the price list has been set as your default price list.
6: Set all the prices to the level you want to.