I've recently set up a new computer using Debian 9.1 . During the initial configuration, I installed the desktop environments Gnome and LXDE.
Presently the system is set up to use Gnome as the (default) desktop. Also, it looks like the window manager is lightdm.
I would like to know how to switch to LXDE. All the other questions I've seen related to this topic hint at how to change the window manager, or how to install a new desktop environment; but I already have the environments I want to work with installed. A best answer would be a mechanism to switch to an arbitrary desktop environment (I might like to try KDE some day).
Some extra notes: This system is headless, while it does have a video display, I'm not using it (I can connect a monitor, but with some difficulty). I connect using SSH, and VNC (Xvnc TigerVNC 1.7.0). When I connect to the VNC server, it starts up a Gnome desktop immediately. During the set up of Debian (after the install), I did have a monitor attached, I don't remember the welcome/login screen ever asking which desktop environment I wanted to use.
TL-DR; How do I switch the default desktop environment between already installed desktops (Gnome,LXDE,KDE,etc) in Debian 9 ?