If your iTunes library is getting too big for your computer , you can consider moving it to an external hard drive.
Here are detailed instructions on how to do this from CNET
This is a big job and the transfer will take a while depending on the size of your library.
There is also a video tutorial available.
Looking for instructions on moving your iTunes library on a mac , here is a great article from Apple , Moving Your iTunes Library
Looking for instructions on moving your iTunes library on Windows , here is a great article from Apple , Moving Your iTunes Library
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