Joomla has come a long way from 1.x to 3.x versions now. Change in version means changes in how Joomla works, change in database tables and possibly change in technology. Depending on the difference between latest version and installed version, it may not be a simple update or install. It may require proper migration of content from old Joomla version to new version. Both Joomla core extensions and any third-party extensions will need to be migrated to new version of Joomla. This includes the template (look & feel) as well so it is also a good opportunity to get a new responsive look & feel for your site.
If you have a Joomla 1.x or 2.x version installed and you need to upgrade to a higher version, contact us. We have vast experience in upgrading Joomla and 3rd party extensions, migrating the database structure, content, template (or designing a customized theme for you) at fixed cost.