how to switch kde and gnome?thanks

I have kde and gnome installed in my debian ,
now it enters gnome when I entered startx,
how can I change to kde
thanks

update-alternatives --config x-session-manager

There are 4 alternatives which provide `x-session-manager'.

Selection Alternative
-----------------------------------------------
1 /usr/bin/icewm-session
2 /usr/bin/startkde
*+ 3 /usr/bin/xfce4-session
4 /usr/bin/gnome-session

Press enter to keep the default[*], or type selection number: 1
Using `/usr/bin/icewm-session' to provide `x-session-manager'.

Thank you!