I know how to install Xubuntu, i.e. by:
sudo apt-get update && sudo apt-get install xubuntu-desktop
I've used Xubuntu, and it's pretty lightweight and is power efficient than Ubuntu. But on the other hand, it does take away the looks of Ubuntu. So, obviously, I wanted to use Ubuntu when I've no limit on power usage (laptop is connected), and Xubuntu when there is a limit (laptop on battery).
So, is there a way to switch back and forth between Xubuntu and Ubuntu, based on convenience?