A while ago I installed Ubuntu 17.10, and now LTS 18.04.1 is out, I want to upgrade to it. I tried to upgrade from Ubuntu 17.10 by typing update-manager -c as the command after I pressed ALT+F2, and while it said that there is LTS 18.04 version available, and asked it I wanted to upgrade, but when I tried to upgrade it gave me an error. Not sure what it was. I am thinking to delete the current version of Ubuntu from the dual boot, and install a fresh version of LST 18.04.1. How safe is it to delete an OS from a dual boot system, and how to do it without missing up the Windows OS? I heard that deleting the occupied part by Ubuntu will miss the Windows OS, and I need the Windows OS CD/DVD and boot in repair Window. But I don't have this CD/DVD. The recovery is part of the Hard Disk. So, basically I am asking: How safe is it to delete an OS from a dual boot system? What is the best way to do it that minimizes the risks of missing the other OS?