I have tried editors like menulibre and lxmed, but whatever I do with this applications, I can't make any changes to the menu.
What can I do?
Arch Linux is the distro.
The best way is for you to work on a local copy of the menu file.
cp /etc/xdg/menus/xfce-applications.menu ~/.config/menus/xfce-applications.menu
Then either edit it by hand or use those GUIs.
Note that maybe they're editing /etc/xdg/menus/applications.menu and that isn't used by Xfce so you have to point them to the right file.
Also the desktop-directories and the applications' desktop files themselves interfere on what shows up or not in the menu, so it depends on what you're trying to do.
Oh wasn't harder than that. Thanks.