The Presto template is installed like any other Joomla template. The downloadable package found in the Joomlabamboo download area is uploaded via the extensions manager in your site's administration.
The document How to install a Joomla template can be followed for more detailed help on installing the Presto template.
The Presto template is available for Joomla 3+ only. While the template may be installable in Joomla 2.5 we recommend only using Joomla 3 with this template as the theme remains untested in Joomla 2.5.