Step 1: Connect the hard drive with Computer
Make sure your hard drive have enough size before moving your iTunes library containing both audio and video files.
Step 2: Select a new location
To do so, open your iTunes preferences under the iTunes Edit menu. With the preferences pane open, click under the ‘Advanced’ tab. Click ‘Change…’ button under ‘iTunes music folder location’ to change the location to a desired folder on your external hard drive.
Step 3: Allow iTunes to Copy new media files
Under the ‘Advanced’ tab make sure you check the option ‘Copy files to iTunes Music folder when adding to library’. This ensures that any new content you download or rip into iTunes gets transferred to the new location. Click ‘OK’ to continue.
Once the preferences are changed, navigate to the iTunes File menu, scroll down to Library, and select ‘Consolidate Library’ from the list of options. This step could take time (depends upon the size of your iTunes library).
Your iTunes library has now migrated to its new location on your external hard drive or flash drive. iTunes have just copied media files to external hard drive and have not deleted from iTunes library Now. To check if the files have been copied to the new location or not, open iTunes, select a song, and select Get Info from the File menu. A window will pop up describing all the attributes of your song file, including the location of the file. If you want that new files should be transferred to external hard drive then make sure the external hard drive is not removed from the computer. If your external hard drive is not connected, iTunes will temporarily default to the original location until your drive is connected again.