How to delete old iPhone backups
Running out of hard disk space on your Mac or Windows PC? If you have (or have had) multiple iPhones, iPod touches or iPads, there’s a very good chance old, unused backup files you no longer need are wasting a significant chunk of otherwise useful space — here’s how to get those gigabytes back.
According to Apple Knowledge Base Article HT1766, when you want to delete a backup created by iTunes (7.5 or later):
• Open iTunes Preferences:
— Mac: Choose iTunes > Preferences
— Windows: Choose Edit > Preferences
• Click Devices (iPhone, iPod touch or iPad does not need to be connected)
• Confirm that you want to remove the selected backup by clicking Delete Backup
• Click OK to close the iTunes Preferences Window
Also, in iTunes 8.1 or later you can view the phone number, IMEI and serial number of a backed up iPhone by hovering the mouse cursor over a listing (see above image), which is a handy way to locate the backup of the specific idevice you want to delete.