Help with changing Computer name, or User name

[RuthN]

Hi, I have just read an article by iMore about the steps that Set-up Assistant takes you through, and I need more help. I tried to post the question there but was told I was not experienced enough or something. so I'm trying again here. This is what I wrote -

Hi there. Please can you help me with a bit more info. I have just set up my new MacBook Air 2018. I also have other Macs with Sierra and High Sierra, so I thought I understood them, but not so sure now!
This new Mac has Mojave on it. When I got to this bit as in your instructions -
'Enter a Full name for your computer. If you signed in with your Apple ID, this will populate automatically.
Enter an Account name. If you signed in with your Apple ID, this will populate automatically. ' - I left my Full Name as my name, I can't remember what I put in for Account name, and I used a password that I know well.
Now the problem is, I didn't realise that what I filled in would then appear as my computer name every time I fire up the machine. I don't want my name, my real name, to appear on my screen, I want my computer name to be something else.
On my other machines, I have already changed the computer name successfully, in Sharing, and in Users&Groups, but on this new machine I get a warning message if I control-click on my Admin account and go to Advanced. I believe maybe you have to make a new Admin account first, but again I don't know how to do that.
Sorry this is a bit long-winded. Hope you can help. Thanks, Ruth

 

[Just_Me_D]

System Settings → Users & Groups

Tap on the lock icon at the bottom of the screen and sign in with your admin account.

Right click on the user whose name you want to change and then select “Advanced Options...”

Read the WARNING therein and then decide if you want to alter the username.