If you installed your theme (or plugin) from the wordpress.org website, you have the advantage of getting update notifications and 1-click updates. When logging into your site’s dashboard and you see an update notice, you can update.
To update, click on one of the few links that gives you the update notice. With themes, you will also find an update notice right on the screenshot:
Click on the text link “Update now” and then you are all done! The same process will be the same for plugins, even for our theme plugin updates.