If the installation stalls and fails to respond after a few minutes, or if WordPress gives you an error message, you are suffering from PHP configuration limits that are set too low to complete the process. You should contact your hosting provider and ask them to increase those limits to a minimum as follows:
You can verify your PHP configuration limits by installing a simple plugin found here: https://wordpress.org/plugins/debug-info/. And you can also check your PHP error logs to see the exact error being returned.
Besides this, you can upload the theme using your FTP client, upload the non-zipped theme folder into the /wp-content/themes/ folder on your server