Indeed, there are several ways to make it, but the easiest way is certainly to transfer all iPhone files and backups from the old computer to the new one. The necessary data is stored in several different locations, and we'll figure out what files to copy and where they go for both Mac OS X and Windows. This guide is aimed for iPhone users, but it also works with an iPad or iPod touch.
Syncing an iPhone with a New Mac by Copying Sync Data1. Quit iTunes and disconnect your iPhone with neither an old computer nor a new one
2. Open the Home folder and copy the following directory from the old computer to the new one, located at "~/Music/iTunes".
Here "abc" is the username and the location is shown below.
3. Now open the user library directory and copy the backups from the old computer to the new one, located at "~/Library/Application Support/MobileSync/" shown below:
4. Copy over iTunes Preferences files as well:
5. Once all files are replaced on the new computer, connect the iPhone to the new Mac and launch iTunes, authorize the new computer and all data are stored in the iTunes of the new Mac.
Syncing an iPhone with a New Windows PC1. For windows 7 users, the instructions are basically the same as above, but the files and folders you are looking to copy are stored in different locations. You'll need to copy the following directories and their contents from the old PC to the new PC:
Here, the "USERNAME" is the user's account name, obviously.
2. For older versions of Windows users, iPhone backups are located at the following location instead:
C:\Documents and Settings\USER\Application Data\Apple Computer\MobileSync\Backup
Now launch iTunes and connect the iPhone, it should synchronize normally without any problem. Just authorize iTunes with your new PC and proceed, you'll be able to sync your iPhone with the new computer without worrying about the loss of data.