Use Shift > View > Show Exact Duplicate Items to reveal the exact duplicates as this is normally a more useful selection. You need to manually select all but one of each repeating group to remove. If the duplicates were added recently sorting on date added and deleting the recent additions can be straightforward, although you'll want to make sure there really two sets of files with the same content before you throw any away otherwise you may find your remaining tracks have been broken by the clean-up process.
Use my DeDuper script if you don't want to do it by hand. Please take note of the warning to backup your library before deduping. See this thread for background.
tt2