Third party software such as Acronis true image can roll your system back to an image you made earlier but I’m going to assume you don’t have that option so:
1. The upgrade makes its own roll back point and If the upgrade fails it should un-install itself but this backup point is disabled as the final step of the upgrade so in the event of success it can’t be removed again… I know that sounds like something a crack-head would design but that’s Microsoft for you.
2. Factory reset (3 times) after which windows 8 will be your system again… assuming it was the system that came with the laptop. Some companies use better software than others so for example Asus has very solid backup software because they market themselves towards...