You can change your shipping address after you place an order as long as the item has not shipped. Typically, you can only do this the same day an order was placed because items are shipped as fast as possible.
If an item has already been processed for shipping, you will not be able to change the address.
To update your shipping address:
1. Log into your account
2. Hover your mouse over your name at the top-right corner of the site
3. Click Purchases from the drop-down menu
4. Click on Details next to the purchase