Changing root's password
In the past, YunoHost had a special "admin" user in addition to root. This is not the case anymore, and each user admin password can be changed via the regular process.
root, a.k.a "god on the machine", still exists however, and being able to access the root account can sometimes be useful. For example, because LDAP (the user database powering YunoHost account) is broken. In this case, you may be able to connect to root via SSH from the local network, via a direct screen/keyboard access, or via a rescue console provided by your VPS provider - depending on the nature of your server.
Using the web administration interfaceβ
First, connect to your web administration.
Then go to Tools > YunoHost settings > Security tab > Change root password
Using the command line interfaceβ
yunohost tools rootpw