To connect an Instagram account to your brand's Facebook timeline, navigate to the Sharing settings (Profile tab > Edit sharing settings) and tap the Facebook button. If you have not yet done so, you will need to connect Instagram to Facebook on your mobile device. When the Facebook authorization page appears, make sure that the Facebook username at the bottom is an administrator of the brand's Facebook account.
If you already connected to Facebook on your device, but need to switch accounts, choose "Logout and unlink account" from the Facebook options page, and reconnect through the instructions above.
At this point, your device will be connected to your Facebook account, and by default, will post to your personal timeline. To change this, tap the "Profile" button in the bottom right of Instagram.
Next tap the Settings icon (looks like a gear) in the top right. Scroll to “Sharing Settings” under Preferences and select Facebook. Then tap “Share Photos To” and from this screen select that page you want to share from.
This will display your posting options, including your personal wall, and a list of any pages for which you are an administrator. Select the page that you would like your Instagram to post photos to.
When you click back, you will see that your brand will replace "Wall (Default)" in the "Share Photos to" category.