When GCI releases a new carrier bundle for your iPhone, you should see the following pop-up.
Click "Update," and your phone will install the new carrier settings.
If you wish to install the settings at a later date, click "Not Now."
You can also check for a new carrier update manually.
Open the Settings app and tap General
Select Software Update
If there's an update available, you'll see an option to update your carrier settings. If you don't see that option, your phone already has the most recent update.