Hi! Thanks for your reply,
In both links, they showed how to install/uninstall distributions installed from the Microsoft store. I didn't use the Microsoft store to install it, instead, I used the command line. I did find a link on one of the pages showing how to install WSL in build 20246 or later, which is using the "wsl --install" command.
I would expect there being a --uninstall option in the wsl command, but there isn't. And I tried turning off WSL in control panel, but that just seemed to free up a few hundred MBs of space. I then got into settings and looked at the Other tab on the storage page, expecting to see a reasonably big folder which contains Ubuntu, but I didn't find one. So probably it is already uninstalled. I'm not too sure.