It is very common that, in an effort to protect privacy, an administrator will have users who only want to be displayed by their usernames.
In order to change SocialEngine 4 from showing the first and last names by default, do the follow:
1. Log into your admin panel and step into a “Profile Questions” page under the “Settings” tab.
2. Delete the “First Name” and “Last Name” profile questions.
3. Re-create both Fields, ensuring the Profile type is set to Single-line Text Input (NOT “First Name” and “Last Name”). If you don’t want these field to be visible on the user’s profile, be sure to select “Hide on Member Profiles”.
4. If you already have existing users, you will need to run the following queries in your MySQL database to clear their display name:
UPDATE engine4_users SET displayname = username;
Make sure to always make a backup of your current site before doing any mods.