You will have to keep in mind that you will not be able to retain ratings and play counts.
You will have to then check for "Consolidate Files" and select OK.
When you have many files which are not in i Tunes Media’s folder, it may take several minutes.
However, there is a possibility that there may be some duplicates of the media files. When in the music library, you can select the Option (ALT) key and go for "Show Exact Duplicate Items".
When this process is over, you would have successfully merged two libraries.
The fine specifics of how to consolidate your i Tunes library may vary slightly depending on which operating system and version of i Tunes you’re running, but variances from the directions given below should be slight.
Music can be stored along with other media on i Tunes.However, libraries that big can take up more space on a hard drive than you may have available--there's one relatively simple solution to your problem.Here's how to keep your huge i Tunes library (and even expand it) while still leaving enough room for important programs and files on your main hard drive.It can get difficult if your library happens to be a huge one.Now you’ll have a library that is derived from playlists taken from two separate libraries.On account of the large size of many i Tunes libraries, it is not easy to consolidate them.