How do I properly uninstall a distro dual-booted with LL 2.0?

[gold_finger]

If LL 2.0 is the distro currently in charge of booting the computer then you have nothing to worry about.  Just boot into LL, use GParted to delete the other distro's partition(s) (make sure they are unmounted first) and run sudo update-grub in an LL terminal to eliminate its entry from the boot menu.

If the other distro is controlling the boot process, then boot into LL 2.0 and install grub to the MBR of the drive so LL takes over boot control.  (sudo grub-install /dev/sda assuming sda is the drive you boot from.)  After rebooting, run sudo update-grub to update the grub menu and get rid of the entry for the now deleted OS.