To Modify one of your Promotions :
In the Main Menu, click on Offers
On the Your Main Offers page, click on the offer you want,
Then click on Modify Prices
Click on the Promotions tab
Then click Modify on the relevant offer line
In the settings screen for the promotion concerned, make all the changes, then Save your page
To delete one of your promotions :
In the Main Menu, click on Offers
On the Your Main Offers page, click on the offer you want,
Then click on Modify Prices
Click on the Promotions tab
Then click Delete on the Promotion line concerned
The promotion is irreversibly deleted