The only way to go is to uninstall 3.5 reboot and then install 3.12. You cannot export your 3.5 configuration to 3.12. You will have to start from scratch.
Sorry to be the bringer of the bad news.
Ok, do you mean that 3.5 is a bad version? Can you please give me the link to Download 3.12?
Would I be OK using Uninstall option from the Menu? Also, I have Norton Firewall which I don't use and never upgraded - could it be a problem as well?