How and when can I change the username and password that was put, when openSusse was installed?

I have had openSusse leap 15.2 installed on my laptop one day ago. But the people that installed it, put as a username: user and as a password: root - they are about the superuser, right?
I have been already told in this forum, that I can change and create new profiles via YaST, but when can I use YaST - only after the first log in.
My question actually is - can I change the superuser username and password with the first log in and if I can - what is the procedure?

Thank you very much in advance for your answers!

Duplicate thread. See

Locking this one.