1. Open your putty then enter your website's IP address only
2. Don't import any keys of SSH then click on Open
3. Enter your Cpanel's username then hit Enter
4. Enter your password then hot on Enter key.
5. Add your Path like public_html/ then Hit enter key.

Then run the following commands to upgrade.

php bin/magento setup:upgrade
php bin/magento cache:flush
php bin/magento cache:clean
php bin/magento setup:static-content:deploy

Do following steps:

1. Open your putty then enter your website's IP address only.
2. Don't import any keys of SSH then click on Open.
3. Enter your Cpanel's username.
4. After insert your password.
5. Add your Path like public_html/.

Then run the following commands to upgrade.

php bin/magento setup:upgrade
php bin/magento cache:flush
php bin/magento cache:clean
php bin/magento setup:static-content:deploy