Stop latest upgrade from installing I  downloaded by accident the latest update by Apple, currently running 10.13.1. 

I can't upgrade to 10.13.2 due to a problem with the GPU which makes it impossible to boot up. 

Right now it's asking to restart in order to install it. Is there a way to stop the installer from running ?

I found the solution here 


Can I delete /Library/Updates on EI Capitan
You should be able to force quit the installer. To do this, press the optioncommandESC keys to bring up the Force Quit Applications window. Then select the installer and click on the Force Quit button.

Another option is to make sure the installer is the active app and then hold down the shiftoptioncommandESC keys for at least three seconds to immediately force quit it.