If you did not start life with an Android phone, adding a "skin" or theme to the Smart Pro keyboard may not be as obvious as the Forum web page text suggests.
You must know that to the right of the keyboard choices are identical "slider" icons on the "Settings" page for Keyboard and Input and THAT ICON in THAT row is the settings they mean for you to click on.
When THAT settings page opens for Smart Keyboard Pro you will see the skins IFF you have placed the zip files in a /skins directory or 'folder' in the root of sdcard0 using a filesystem tool.
The 'forum' page should have an image of the entry Settings page so that you can SEE what they mean. The keyboard would be so much better if there were an option to have a Settings key as a long click option !