Change admin username

Hello all,
I just installed NextCloudPi on a Raspberry Pi.
However, I would like to change my username (I am admin).
How do I do that?
Thanks for the help

It’s Linux…
Create a new user account, assign admin rights to the account.
Login as the new user and delete the old (admin) user…

Thank you, it worked.
But now I can’t get into the Control Web Panel.
What can I do now?