Change of Display Manager
/etc/sysconfig/displaymanager with a text editor.
Display Manager can be changed at line
Display Manager also called Login Manager can be modified as explained previously.
Main managers are:
For more manager, see here.
If you have trouble with a manager you can temporarily replace it with
Change of Window Manager
To change of window manager laso called desktop manager, open
XXX with one of these manager : gnome, kde, xfce, lxde, enlightenment, icewm, cinnamon.
The a reboot it's needed.