Iphone 5s unlock to make all providers available
If your iPhone was purchased on a contract, you must contact your provider for them to release your iPhone from their network lock. This is generally put in place to ensure users on a contract do not switch carriers after paying only one or so instalment for the phone.

If you have finished your contract, purchased the phone outright, or come to an agreement with your carrier to unlock your device you'll need to backup (if needed) and restore your device through iTunes to apply the new unlocked carrier settings. You can contact Apple to see if your device will be unlocked after restoring if you're not sure.

There may be other ways around this unlocking process, however none are official or supported by Apple. Nor are they guaranteed to work.