If you are going to install the theme using FTP, you would require an FTP Client, such as FileZilla.
To install this theme you must have a latest version of WordPress already installed. For information in regard to installing the WordPress platform, please see the WordPress Codex –http://codex.wordpress.org/Installing_WordPress
Step 1: Download the installable theme from your Themeforest/Codecanyon Downloads page, you will get an zip archive.
Step 2: Log into your hosting space (server) via FTP client.
Step 3: Extract your downloaded theme zip archive so you can upload the whole extracted folder to your hosting.
Step 4: Navigate to this path in your server…/wp-content/themes/ and upload the Theme folder.
Step 5: Login to your WordPress Dashboard and go to Appearance > Themes and activate the newly uploaded Theme.