since it is a single boot sytem; just befor the splash screen that has the Kubuntu logo with a progress meter at the bottom, You should see a black screen with some white text. At the end of the last line you should see a count down timer. That timer starts at 3, which means 3 seconds. At that point befor the timer hits 1 press <enter>. That will stop the timmer. Next follow the instuctions from earlier.
My question for you is: If you are new to linux why are you using root anyways? By default Kubuntu will not let you log in as root. If you need to do something as root then hit ctrl + F2. At that point type log in as yourself and type in sudo su. it will promt for a password (which is your user password). At that point you will be root on the cli (command line interface) only. BTW if you do the ctrl + F2, to get back to the desktop hit ctrl + F7.
Advice for you: Since you are new to linux DO NOT fall for the rm -r / command as root. That will delete your entire system with no recovery option. Also the Ubuntu family version system is easy to learn. The number to the left of the period is the year in which it was made, and the number to the right is the month it was released. Connical only releases in april or october (every 6 months) maybe that will help know what version you got. So you are more than likely on 8.10 not 8.1.
I hope that is helpful.