Release upgrade from within a Wubi install.
Verify that there are no wubi-specific problems with kernel and bootloader upgrading.
Download wubi.exe for the previous supported release from http://releases.ubuntu.com.
- Install Ubuntu desktop under Wubi.
Run update-manager -d -c from a terminal
- Click the upgrade version button
- Watch it upgrade, noting any errors
- After upgrade, reboot to confirm that the system still boots correctly to the desktop.
- Reboot to Windows as well to verify that this still works.