1. This is not a standalone app, you need to download the LATEST version of GO SMS Pro app in order to apply this theme. (Search “GO SMS Pro” to download)
2. To apply the theme within GO SMS Pro,download it from Menu->Settings->Appearance Settings->Theme shop(or Plug-in UI->Theme shop). After downloaded, it will displayed in "Installed themes" Tab, click and apply it.
GO SMS Pro theme gosmstheme