A few months ago, I quit Windows altogether and moved to Lubuntu 18.04, but for some reason I couldn't use the trash can, so here's what to do at the time.
When I tried to move the file to the trash, I got an error for some reason (I forgot to write down the content of the important error). It was a phenomenon that I could not move the file to the trash.
The remedy was very simple. That is, delete the trash folder as root and recreate the trash folder with normal privileges.
Normally, the trash directory is located in "~ / .local / share", so open it first. For Lubuntu, the standard file manager is PCManFM, so you can do the following:
sudo pcmanfm ~/.local/share
There is a "Trash" folder there. That is the trash folder in question. Delete that folder. At this time, since the trash can is not functioning normally, it can be completely deleted by pressing the Delete key while pressing the Shift key, so it is completely deleted by this method.
Now move to the "~ / .local / share" directory with normal permissions. If you can move it, create a folder named "Trash" there. This is the end.
Log out, log in again, and put the appropriate files in the trash. If it works, you should have the data there and empty the trash.