Download the files from https://www.posersoftware.com/downloads first, then install the main update (the Install Poser 11. exe file). It will ask you if you want to uninstall--choose that you do but you want to retain your existing preferences and all should go smoothly. Make sure you install the support files as well. Do make sure you read the instruction screens as they come up and not just click 'ok' reflexively.