If you have not made any changes to the theme files, you can just copy over the new files into the theme directory. Make sure you take a backup of the directory, just in case you need to revert back.
I usually take a backup, delete the old one and create the new one with all the new files. Make sure you do not use wordpress during this process, otherwise it may switch to the default theme twenty twelve. Any customizations in wordpress admin (widgets, menus, settings etc.), options in theme options panel should remain intact without issues. If you have modified custom.css file, do restore it after the new theme version is copied over.
You can download the update from your downloads page listed in your profile drop down menu.