I have a Windows 10 machine and want to install Ubuntu 16.04 or 18.04 using a DVD drive but when I boot, at step 4, I didn't get the option of Install Ubuntu alongside windows boot manager, so I chose Something else and clicked Continue.
In the next step when I select unusable and trying to click +, the + button is disabled. Similarly, the _ and Change button are disabled as well.
How should I proceed?
