Some premium or custom WordPress plugins may not allow you to update from within WordPress. In this case, you'll need to upload a copy of the newest version's files using FTP.

Connect to your hosting with FTP.

Navigate to the directory containing your WordPress site.

Upload your plugin to the /wp-content/plugins directory.

If your plugin is zipped, you will need to unzip it.

Note: If you do not have a way to unzip the file on the server, you will have to unzip the file locally and then upload the unzipped directory of files.

Your plugin should now be updated.