Download and unzip the software, if the latter isn’t done automatically. The resulting folder contains the main script Poserframes.jsx and a folder with a number of Photoshop action sets in the form of files ending in .atn.
Copy the script Poserframes.jsx to Photoshop’s scripts folder. On Mac it’s in /Applications/Photoshop 202x/Presets/Scripts and on Windows 10 it’s in C:\Program Files\Adobe\Adobe Photoshop 202x\Presets\Scripts. You may have to change the permissions of this folder to copy the script there.
Restart Photoshop and make sure Poserframes shows up in the menu File/Automate.
Install the Photoshop actions by double-clicking on the action files ending in .atn, or by clicking on the hamburger menu in the actions palette in Photoshop, choosing Load Actions… and then select all action files and click on Open.
If you want to update Poserframes you simply download the new version, replace Poserframes.jsx in Photoshop’s scripts folder and replace your installed actions with the new ones.