User blog comment:SuperWikiGenius/Help/@comment-68.55.64.202-20120522030006/@comment-4650581-20120716000909

You would have to do this manually by copying it to a usb after your done playing ever time or by zipping it and uploading to a cloud service every time. Just go to your minecraft (or if your playing with a mod pack the techniclauncher folder then the appropriate modpack) and go to your saves folder. Sadly there is no way to automatically do this.