How to dynamically change themes after clicking a drop down menu of themes

Fiddle:http://jsfiddle.net/82AsF/ (click the themes dropdown in the navbar)
Give your links a class theme-link and a data-theme value of the theme name like so:

<a href="#" data-theme="amelia" class="theme-link">Amelia</a>

Then, define your themes in a global variable like so:

var themes = {
    "default": "//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css",
    "amelia" : "//bootswatch.com/amelia/bootstrap.min.css",
    "cerulean" : "//bootswatch.com/cerulean/bootstrap.min.css",
    "cosmo" : "//bootswatch.com/cosmo/bootstrap.min.css",
    "cyborg" : "//bootswatch.com/cyborg/bootstrap.min.css",
    "flatly" : "//bootswatch.com/flatly/bootstrap.min.css",
    "journal" : "//bootswatch.com/journal/bootstrap.min.css",
    "readable" : "//bootswatch.com/readable/bootstrap.min.css",
    "simplex" : "//bootswatch.com/simplex/bootstrap.min.css",
    "slate" : "//bootswatch.com/slate/bootstrap.min.css",
    "spacelab" : "//bootswatch.com/spacelab/bootstrap.min.css",
    "united" : "//bootswatch.com/united/bootstrap.min.css"
}

(please host these bootswatch css files on your own server when you do this - I'm only hotlinking because I don't have a server on hand)
Then, use the following jQuery code:

$(function(){
   var themesheet = $('<link href="'+themes['default']+'" rel="stylesheet" />');
    themesheet.appendTo('head');
    $('.theme-link').click(function(){
       var themeurl = themes[$(this).attr('data-theme')]; 
        themesheet.attr('href',themeurl);
    });
});

the main problem with above solution if page is refreshed the theme is gone. i found this article very helpful regarding persistent theme in the browser because it save setting in browser's storage.

i hope it helps you

http://wdtz.org/bootswatch-theme-selector.html