Then, install CWM for HTC One by following this post. After that, download the root toolkit from here. Make sure not to rename the folder. Extract it and run the program included in the folder. The toolkit automates everything – from rooting your phone to installing SuperSU – everything is done automatically, just with one click.
Rooting will allow you to access forbidden parts of the OS, such as system files. It will also let you patch games and whatnot.