Is Ubuntu only designed for terminal usage?
NO. You could open file manager and press del.
inside file manager right click a file/folder see properties see permissions.. if you’re not the owner of the file/folder you cant do various things with it see Lubuntu file permission.
same thing using terminal
<open.terminal>
sudo rm -rf /opt/lampp/htdocs/<folder.or.file.to.delete>
<enter.root.password.at.prompt>
or use mc
<open.terminal>
sudo apt update
sudo apt install mc
sudo mc
<navigate.to.your.file.folder>
<select.it.and.press.F8.to.delete.it>
or you can run file manager as root.. same procedure as mc
inside Linux most of the files don’t belong to user.you(as in windows) so you you cant do various jobs on them, see