Well yes and no. It's not impossible, but in most cases it needs that you reboot and then boot from a media that has the installation inside; this would break your ssh connection. In order to have it working, you'd have to have the installation media on your harddrive, and use a desktop-startable installation program (like that of Ubuntu/Kubuntu/Xubuntu's) which would allow you to install the OS using a graphical window on your desktop. Then just make sure the bootloader options are fine and make it restart; the problem then would be, you couldn't get an ssh connection during the boot process, so one of the OSes would be booted depending which one was default, and if it was the new one - without sshd or configurations or normal user accounts - you couldn't login via ssh. This can be prevented by configuring the bootloader to boot the OS of your choice, and before rebooting, edit the configurations of the other Linux so that sshd is started and configure it so that you can login -- and create user accounts, of course.
So, it can be done, but using an ssh connection only it might be tricky for a beginner.