Avinode cannot in any way access the credentials on user accounts, only the user themselves have access to them.
If you want to change your name you can do it by going to the profile icon in the top right corner, then choose My profile. Under Personal Info you can update your name and under Sign-in & Security you can update your credentials.
If an employee have left your company, the administrator for your account should delete the user account and create a brand new one if anyone else need access to Avinode instead. You should never rename an existing account (unless spelled incorrectly).
Renaming an account will cause problems going forward ie. you will not be able to change the security email and thereby ask for a new password.