Make a change to one product in the Project Editor. In this example, I opened the top Item and changed the Labor Hours to 2.
Select the Item you edited then select any other similar Items that you want to update using Ctrl or Shift on your keyboard and then click Similar->Products/Labor, depending on what you've edited.
You will get a message explaining what's about to happen.
All Options are checked by default. Choose what you want to update. In this example only Labor Hours is selected: