There are installation guidance in both the
project WiKi and in the sticky threads at the top of the KOReader Forum here. The "installation" of KOReader is just a matter of copying over the KOReader folder, from the download, into the .adds folder on your device. The installation of KSM8 and any needed updates (depending on the Kobo firmware on your device) takes more consideration but is well explained in the KSM8 thread.
KOReader is not likely to "break" by the Kobo firmware updates, but KSM may be affected and need reinstallation or even a new update, to work with the firmware change.
Luck;
Ken