Change Run level in CentOS

Linux run level has been configured in inittab which located in /etc/inittab
by default all linux has runlevel 5

#vi /etc/inittab

# inittab is only used by upstart for the default runlevel.
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:

If you want to change the run level then edit the following line

id:3:initdefault:

Save the file and reboot the machine

After reboot you have the CLI mode. how to go GUI again

#startx

Manually change GUI to CLI

#switchdesk kde    // from gnome to kde

#startx  

#switchdesk gnome    //from kde to gnome

#startx