I'm not a 100% if this would work if you're currently still running ICS. I'd hope a more experience developer would confirm the ICS side of things before you try it, but once your on JB. But you would need to download the back up, place it on your SD card, be rooted, and running Hashcode's Safe Strap then you would Power Off and Turn on your phone. Hit the menu key to open safe strap. Click the recover button, locate the back up file you placed on your SD card earlier and start it. Once the process is finished you would reboot your phone and you should be running JB with root/tether.
Note the above instructions would delete all your apps and personal data so back up with Titanium Backup before trying.