Install the eXtro TemplateSwitcher in your Joomla backend by clicking on extensions -> installation and uploading the zip files.
After the plugin and module are installed, activate the plugin by clicking on extensions -> plugins, choose the eXtro TemplateSwitcher plugin and activate it. Next, click on extensions -> modules and select the eXtro TemplateSwitcher module.
At the options section, choose the templates you want to be switchable in the frontend. You can select multiple templates from the list by ctrl-clicking the respective templates. Only the templates you have selected will be switchable in the frontend, the others cannot be chosen by the frontend user. This prevents templates being displayed that are still in development.
Choose 'on all pages' as menu assignment, so the eXtro TemplateSwitcher module will be always displayed.
At details, you should choose a module position which is present in all templates. If there is no mutual module position for all templates, you should create a separate eXtro TemplateSwitcher module for each template you want to be selectable in the frontend.
In the frontend, you will see a rotating cog in the left upper corner (traditional mode) or a cog in the left lower corner (new mode). This is a trigger - click this cog, and a menu will slide out which lets you switch your templates.
If you cannot click the cog, then most likely, your template uses relative/absolute positioned containers and it produces a z-index issue. Raise the z-index value of the TemplateSwitcher trigger (as described in the FAQ) so it can be clicked correctly.
This module is compatible with Joomla 2.5.x and 3.x . All templated based on the default Joomla template system can be switched. Please note: Templates based on the Gantry Framework are incompatible and therefore cannot be switched, since the Gantry framework extends the default Joomla template system.