Hello there, @audrey_p ...
The resources in that particular thread were from 2019 when the Canvas Community platform was utilizing a different interface. Last Summer 2020, the Community site transitioned to the platform that you see today. So, those directions are not valid from 2019. When you are logged into the Community, you can click on your avatar image at the top right corner of the screen, and then click on "My settings". On the next screen, the words "Personal" and "Username" should have a thin red line under them. Do you see a box to change your "Username"? Please see What are the Canvas Community guidelines? for additional information (in particular, the "Be you" section).
Please let Community members know if you have any other questions about this...thanks!