Welcome to Vodafone Community
No worries @garetbe
One of the Vodafone Social Media Team Members should be along soon or pop them a DM on Twitter or post on Facebook and link back to your thread here and they'll help.
Current Phone > Samsung Note 20 Ultra 5G - SM9860 Snapdragon.
Samsung One Ui 2.5 / Android 10.
As you do not yet have sufficient priviliges to unlock the change user name in your settings, the quickest way to get this changed is to put the user name you would like on the thread.
You can, if you wish, just open a new account with the user name you would like but that would mean using a different email address to the original.