Yunohost has an administrator web interface. The other way to administrate your Yunohost install is through the command line.
You can access your administrator web interface at this address: https://example.org/yunohost/admin (replace 'example.org' with your own domain name)
To reset the admin password (as root) :
$ yunohost-reset-ldap-password
A temporary password will be created, which you can use to define the new password.
To change an application folder, only a few commands are needed: move content, create a symlink and set access rights.
Sample with WordPress:
# Move wordpress folder to an external hard drive
$ sudo mv /var/www/wordpress /media/externalharddrive
# Symbolic link
$ sudo ln -s /media/externalharddrive/wordpress /var/www/wordpress
# Folder must belong to www-data
$ sudo chown -R www-data:www-data /media/externalharddrive/wordpress