This is done by running the program PhotoshopPluginInstaller. You can find this in the installation folder for PortraitPro Body Studio, but the easiest way to run it is by running the installer for PortraitPro Body Studio to re-install everything again, which includes the installer for the plug-in.
The plug-in installer 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 PortraitPro Body Studio gives you is correct for the version of Photoshop that you want to use.
On a Mac, the Elements Plug-In directory is normally:
/Applications/Adobe Photoshop Elements/Plug-Ins
For Windows, the Photoshop Elements Plug-in folder is normally
C:\Program Files\Adobe\Adobe Photoshop Elements (64 bit)\Plug-Ins
C:\Program Files(x86)\Adobe\Adobe Photoshop Elements\Plug-Ins
When launching Elements, make sure that you launch the Elements where you have installed the plug-in. If you launch a different Elements, that will not have the plug-in installed, and PortraitPro Body Studio won't show up in the menu.
On a Mac, this is usually where to find Photoshop Elements:
/Applications/Adobe Photoshop Elements
For Windows, this is usually where to find Photoshop Elements:
C:\Program Files\Adobe\Adobe Photoshop Elements (64 bit)
C:\Program Files(x86)\Adobe\Adobe Photoshop Elements
Elements needs to be restarted before it will use a new plug-in. When the plug-in is installed, you can see it in Elements 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 Body Studio plug-in.