Once you have created a Product Group, you can then use it with a Promotion to change the price of the products in that Product Group.
- Make sure you create the Product Group first.
- Go to Promotions then 'Create new Promotion' in the left hand navigation menu
- Create the promotion - further instructions are available in this FAQ
- When it comes time to choose which products to apply the promotion to, choose the Product Group from the drop down.
- Click 'Create promotion'.