Download the latest package of the theme, unpack the files, and upload the theme on the server.
You need to upload the theme on your server by following these steps–
1) Login to your Hosting
2) Go to public_html > wp-content > themes
3) Upload the updated zip file of your theme
4) Delete the theme of the present version
5) unzip the updated version of the theme
6) After unzip, you may delete the theme zip