change Style Sheet by programming

Hi, I'm creating a Class which should allow user to setup the default theme CSS file he would like to use to render a class object. therefore i have a simple function : public function SetTheme(string $ThemeName) {

       $this->m_ThemeUsed = $ThemeName;

} which set the theme (CSS file) to use to render my object. However, how can i tell to my class to render or update his render with new CSS file theme ? can it be possible to provoke something like a refresh ? Or it is only a CSS or JS topic ? thanks a lot, -- Alain ------------------------------------ Windows XP SP2 PostgreSQL 8.1.4 Apache 2.0.58 PHP 5