Backers have the ability to go back into their survey and edit their address until the point that their survey is locked and exported by the campaign owner.
For a backer to change their address, they simply need to go back into the survey URL and click 'Edit Shipping Address' at the bottom of the page.
**Backers will not be able to change their country. The will need to unlock their survey and complete it again with the correct country to ensure they are charged any additional shipping rates for that particular country**
If you are trying to edit an address for a backer after the survey has been locked, you can go into the backer profile and click 'Edit' next to their address: