Maybe your connection is not fast enough or just not reliable to perform the upgrade.
Well, you can always upgrade using a CD/DVD ISO image.
Of course you do not need to burn the actual CD or DVD.
Once mounted, an ISO is no different than the real thing, in this case.
If I'm not wrong, Ubuntu supports upgrades between 2 LTS versions.If you boot from a live CD or DVD (non-rewriteable) and then run sudo apt-get update and sudo apt-get upgrade or tried to install a package that isn't already on the CD what would happen? If you wish to boot a Live CD and make permanent changes on an existing installation already on a partition, you can 'chroot' and then run the commands. You can update existing apps on the Live CD and install new packages, but they are not persistent - they will not 'survive' a reboot of the CD.If you are more of a GUI than of a CLI type, then you can mount the image by installing either of these two applications (both in the standard repos and they are substantially identical to your purpose): If what you want to do is an upgrade to version 9.10, the very first thing to do is a full backup, of course.
If you want to save yourself from burning a CD, but have some SD memory card around, you can try to put the ISO as the operating system card on the SD card, and boot from it.Some people are recommending a clean install, instead.