Hi - you need to turn off automatic updates in Rhino Options > Updates and Statistics. Then uninstall Rhino 6. When you then install SR12, you shouldn’t automatically be prompted to update to SR13.
Note that the issue you are facing won’t get fixed if we can’t work with you to get SR13 running on your system. Your Intel GPU has old drivers, please open the Notifications panel in Rhino and check the Intel notification - the link there will point you to the Intel website where you can download up-to-date drivers.
CC: @brian