Templates can be updated via FTP. Simply select the template folder on your PC and upload it to your server, using your favorite FTP software. Be sure you upload the template folder to the directory: /path_to_joomla/templates/ – where /path_to_joomla/ is the location of your Joomla! installation on the server.
Note: Do not try to use FTP to install Components, Modules and Plugins if you are a beginner/novice. These items need database entries which have to be inserted manually if you bypass the package installer.