When you first create your SL account you are required to choose a name for your avatar. This is called the username and is the name you use to log in with. By default it is also the name shown above your head.
Now it may be that you were hasty in choosing it or the name you wanted was already being used. Don’t worry because you can change the name that you display to the world; your display name.
Open your profile, Avatar > Profile, and select the spanner icon next to your name (see image below).
Note that your display name can only be changed once a week but for good continuity with the people you engage with inworld, it really is best if you decide on one name and stick to it.
IMPORTANT: At the end of this coming Wednesday’s session I will be creating individual skybox workspace platforms on Koru for each of you. Each platform will have a personalised TP up to it so it would be good to have your display names finalised by then.