First of all, you need to download the theme installable file from your account that purchased item, go to your Dashboard > Downloads Tab
Now go to your site Dashboard
Step 1: Navigate to Appearance > Themes
Step 2: Click Add New, then click Upload Theme > Choose File
Step 3: Navigate to the .zip file on your computer, then click Install Now
Step 4: When the installation completes, click Activate. You will be redirected to the Themes page with Cantab activated.
Step 1: Unzip zip file package – the zip package is inside the Cantab files folder you have downloaded from EnvyTheme Cantab.
Step 2: Connect to your FTP server and navigate to the folder where your WordPress is installed
Step 3: Go to wp-content/themes/ and upload theme folder (the path will look like this: wp-content/themes/cantab)
Step 4: Open the WordPress admin panel (navigate through the web browser to the folder where you have installed WordPress e.g www.yourdomain.com/wp-admin/) and go Appearance > Themes on the admin sidebar. Activate Cantab.