Yes you upgraded your server and Imagemagick is not installed or at least installed where you are telling the program it is.
You can either install Imagemagick on the server and update the path in config settings in our admin and you should be able to upload or in Global Options in admin set your processor to GD2 and see if your able to upload. You can check to see if your server has GD2 by viewing the PHPINFO in admin link.