Hi Mark… the original download link you get (hopefully you did not lose that) is what you use to re-download updates. Unzip it, then also unzip the theme file as well. You will need to use an FTP program to upload and replace the existing theme files. So if your theme is Celestial Reloaded, the theme after unzipping it creates a folder called “celestial” which contains all the theme files in it (make sure they are there). Then using your FTP program, you upload that “celestial” folder to here:
wp-content >> themes >>
You will overwrite the existing “celestial” folder that is there.