This mod?

The instructions are in the mod page. You need OpenIV. You put it in Edit Mode.
You take all the files in the downloaded folder (not the folder itself), hit Ctrl A or Select All, and drag them to the folder below.
You will want to backup your files first (or restore them from games folder) in case you don't like the mod - there is no undo, no uninstall.

Replace the files in:

However, what it should read is

You want to install in your mods folder, not the game folder.