how do i change a user's first name in 365 admin center ?

 To change a user's first name in the Microsoft 365 admin center, navigate to Users > Active users, select the user, then on the Account tab, choose Manage contact information to edit the "First name" field and select Save changes. 

Step-by-step guide

1. Sign in to the Microsoft 365 admin center.
2. Go to Users > Active users.
3. Select the user's name from the list.
4. In the user's details pane that appears, go to the Account tab.
5. Select Manage contact information.
6. Update the "First name" field with the new name.
7. Select Save changes