Do you mean your return policy? You can change your return policy directly on your listing. On the advanced listing form it is just under the payment section.
Or if you want to change all listings, you can do that in bulk edit.
In sellers hub go to active listings. Click the box next to Actions and then click on Edit above that and edit all listings.
On the bulk edit page, check off which listings you want to edit and then at the top click on edit fields - return policy.
I know that there is one other place to change the return policy but I can never find it.
