You don't have to keep uninstalling and reinstalling to do this. Xubuntu Lubuntu and Ubuntu are all exactly the same thing but with different desktop environments installed. Unfortunately Ubuntu is aimed at the attention deficit and those that think phones and tablets are also computers, they're not giving you the proper names of the desktops.
Xubuntu = XFCE desktop
Lubuntu = LXDE desktop.
As I mentioned in a post above, you can install any or all of these desktops and switch back and forth between them at will. The trouble is you need to know the proper name of the desktop environment in order to install it. The stupid software installer program in Ubuntu is designed to look and feel like Google Play Store, completely useless to anyone except advertisers.
There's a much more useful package manager called Synaptic:
sudo apt-get install synaptic
At least with synaptic you can search lists of programs in different categories. Because you're using an older machine I still recommend that you have a look at some of these:
https://fedoraproject.org/spins/