Question: how to install xfwm4 theme?
Answer: Download your archive and unzip it. tar zxvf mytheme.tar.gz.
become root. su &#91;enter root passwort&#93;
copy the theme you've downloaded into the xfwm4 theme folder. ... 
choose the theme from the xfce settings dialog with a click on the settings icon in the panel and then a click on Window Manager.