This is done in the menu of PortraitPro Studio or PortraitPro Studio Max. Choose the Preferences option. Then go to the Plugin tab.
Press the button "Run Plug-in Installer".
PortraitPro will detect what version of Photoshop you have installed, and automatically find the Plug-Ins folder for you. However, if the correct place is not detected you can manually browse to the Plug-Ins folder of the Photoshop you want to use. Please make sure to check that the installation folder that Portrait Pro gives you is correct for the version of Photoshop that you want to use.
The Photoshop CS6 Plug-In directory is normally:
/Applications/Adobe Photoshop CS6/Plug-Ins
When launching Photoshop, make sure that you launch the Photoshop where you have installed the plug-in. If you launch a different Photoshop, that will not have the plug-in installed, and PortraitPro won't show up in the menu.
This is usually where to find Photoshop CS6:
/Applications/Adobe Photoshop CS6
Photoshop needs to be restarted before it will use a new plug-in. When the plug-in is installed, you can see it in Photoshop by selecting the Filter menu option. Look down the list of filters and at the end will an entry "Anthropics". Choose this and you will see it expand to show the PortraitPro plug-in.