On a Mac, the traditional way to uninstall is simply to drag the application to the trash. You can do so with LE, but if you would like to see more precisely what is being trashed you might want to download & install an app like App Cleaner, which is free. Launch App Cleaner, drag the LE app into its window and you will then see all the files associated with LE which will be deleted if you choose to do so:
If you agree with all the the options press the Delete button; if not, press Cancel or deselect whichever files you want to keep.
You will note that no songs are included in the delete list. I'm not sure where you've been storing your song data, but it's wise to keep them on an external drive from the beginning. If they are not stored externally already, create a folder on your external media then drag&drop them. If you have songs with any linked (not imported) audio files, it's possible you may need to re-link them. I would suggest testing one or two first.