Using comforto directory found inside of comforto.zip file located inside ZIP file you downloaded from ThemeForest.net you should perform the following steps:

• Using FTP client you should login to server where your WordPress web site is hosted
• Using FTP client you should navigate to /wp-content/themes/ directory under your WordPress web site’s root directory
• Using FTP client upload comforto directory to themes directory on remote server
• Once installation is complete you can activate Comforto theme here:  WP Dashboard → Appearance → Themes