Find the files in ~/.local/share/applications
OR
Download and install lxmed. However lxmed was not designed originally for the XFCE menu and so it does not see some of the menu entries and generally speaking does not always work.
… and why the otherwise awesome XFCE has no standard menu editor out of the box — or better yet, the ability to right-click and edit/delete an item in the menu — that is beyond me.
Here’s a nice article on this subject btw:
https://wiki.xfce.org/howto/customize-menu