Installation Instructions

J 'ais strongly regretted the lack of installation instructions.
Faut'il run from the existing OS or boot the computer from the DVD ??
As it was an update, I 'ais chose the first method, as the installation software did not ask me to remove the DVD, rebooted the PC and wondered (with ??) if I wanted to boot from the DVD I did not do it, except the final where I restart the ais done. And apparently the software has reinstalled windows 8 from the beginning. Should he choose the 2nd method from the start ???