stylesheet switching

first you need a theme switcherplugin an activate it in youre plugin list. You need to have a code in youre template something like this
if (function_exists(‘wp_theme_switcher’)) { ?>
<h2>Styleswitcher</h2>
php wp_theme_switcher(); with the needed tags.

Then you can manage youre themes in youre themeswitch options.
The themeswitcher you wil find on the pluginlist from WP.