How can I use my iPhone to update my Facebook username?

How can I use my iPhone to update my Facebook username? What are the procedures for changing the display name of my profile using the Facebook mobile app? Are there any restrictions or things to keep in mind when I make this change?
I’m asking those who are experienced with the procedure for guidance and tips.

  1. Open Facebook on your mobile device.
  2. Tap Menu in the top right.
  3. Tap Settings & privacy, then tap Settings.
  4. Tap Accounts Center, then tap Profiles.
  5. Choose a profile, then tap Username.

I can only find an option to “change username,” not one for “how to change your name on Facebook.”