If  you have a limited storage on you Mac (or Pc) you might want to have your iTunes Library on an external HD. Follow this TUTORIAL HERE to do that. If you’d like to have your library with you though, there are a couple of things you could do:

 

Move your Mobile Sync folder

The MobileSync folder is used by iTunes to backup your iOS devices (iPod, iPhone, IPad, etc.) and if you have a couple of these devices, it can grow to a very large size and take up a good amount of disk space on your Hard Drive.

1. Copy or move your ~/Library/Application Support/MobileSync folder to your external Hard Drive.
2. Now open Terminal and run the following command, replacing <Your External HDD> with the name of your actual external Hard Drive [tip: drag the external hard drive icon into the terminal and the location will be automatically added]

ln -s /Volumes/<Your External HDD>/MobileSync ~/Library/Application\ Support/MobileSync

This is creating a symbolic link for the ~/Library/Application\ Support/MobileSync folder that points to the external harrdrive MobileSync folder and from iTunes point of view, nothing has changed and it works as normal

 

Delete old iPhone/ iPad backups inside iTunes

1. Open iTunes on your Mac or Windows PC
2. From the menu, Click on Preferences and click on the Devices Tab

1. You’ll see a list of all the iOS devices backed up to iTunes, along with the data of the backup.
2. Select the old ones you want to delete. Click on Delete Backup…
3. You’ll be prompted to confirm the deletion. Click Delete.