We turned on automated update for PowerGUI 1.9. If you are running an earlier version of PowerGUI, your computer is connected to the internet, and the Automatically check for product updates checkbox in Tools / Options is selected you will be prompted to upgrade the tool.
You can obviously also do this manually by downloading PowerGUI here.
One small confession to make, is that if you were among the first users to download PowerGUI 1.9 when it got out, you might still be prompted for the upgrade. This is because due to our internal process issue, initially we posted one of our RC builds (build 900) instead of the RTM one (902). Because we do not support upgrades between beta builds of the same version, if you are affected you will have to manually uninstall 188.8.131.520 and then install 184.108.40.2062 instead. All your settings and customizations will be preserved. Sorry for inconvenience if you were affected.