I am trying to edit my music list and then sync it to my iPhone 5 so I don't run out of storage space. However, I see the check marks on the iTunes library but am unable to uncheck them? How do I manually edit what will be synced to my phone?
You uncheck the music in your iTunes library on your computer and along with sync only checked songs and videos selected under the Summary selection for your iPhone sync preferences with iTunes, only checked songs in your iTunes library will be transferred to your iPhone or remain on your iPhone and the unchecked songs in your iTunes library that are currently on your iPhone will be removed when syncing.
Or make use of iTunes playlists and choose selected playlists, albums, artists under the Music selection for your iPhone sync preferences with iTunes and select the playlists below that you want transferred to your iPhone.