Use iTunes Consolidate Library Option
If you have music all over your hard drive, you can organize your music by dragging and dropping the songs into the appropriate folder. However, iTunes offers a simple, albeit somewhat ineffective, way to locate all of your tunes and copy them to the iTunes folder. Once they are copied to the folder, you can organize and categorize to your heart’s content.
Unfortunately, you may have noticed that the word “copy" was used in the previous paragraph instead of the word “move." As you might guess, when a file is copied, it makes a duplicate of the file. That’s unnecessary data, and to get rid of it once the files are copied, you’ll have to spend some time deleting these duplicate files from your hard drive. However, by consolidating, you’ll have all of your files in one place, making backing up your entire music library much easier.
To consolidate all of the music files located outside of the iTunes Music folder and place copies of them in your iTunes Music folder, perform the following steps:
1. Open iTunes.
2. Choose Advanced>Consolidate Library.
3. Accept the warning shown by clicking Consolidate.