1) Unzip the downloaded file.
2) Create a folder "mrelwood" in the REAPER data folder in:
3) Move or copy the unzipped content (file(s) and folder(s)) to the folder "mrelwood" that you created in step 2.
4) Restart REAPER (or press F5 in the "Add FX" menu / plugin list) and the new plugins will show up.
Note: If you have installed REAPER in an unusual location, the data folder can be located via REAPER's "Options" menu item:
"Show REAPER resource path in explorer/finder..."