Like most Blender Add-ons, you install Faceit in the User Preferences.
Edit > Preferences > Add-ons > Install
Faceit comes in a .Zip folder. You do not have to unpack it. Simply click the
Install button and browse the filepath to wherever you saved your Faceit copy.
Afterwards you will need to enable the Add-on by clicking the enable checkbox.
See the images attatched below.
To update, simply follow the installation steps and overwrite the current installation.
It might be necessary to restart Blender for an Update to take effect.
Install or Update the Add-on
Enable the Add-on
Find the Add-on in 3D view (N-Panel)