Here’s how you can manually install your plugin if somehow you can’t install plugin via WordPress.
Step 1 : Download your WordPress plugin.
Step 2 : Extract your plugin file.
Step 3 : With your FTP program, upload the plugin folder to the
wp-content/plugins folder in your WordPress directory online.
Step 4 : Go to Plugins screen on your WordPress Dashboard and find the newly uploaded Plugin in the list.
Step 5 : Click Activate Plugin to activate it.