WordPress since version 2.5 has released a option for users to upgrade automatically but with the use of FTP login info everytime you try to upgrade plugins or wordpress core. But there is a simple trick to remove this prompt and just upgrade without the FTP login input everytime.
For this you have to login to your wordpress blogs root folder with your FTP tool like Filezilla, cuteftp etc. Then search for wp-config.php and add the following code at the end of the page.
define(‘FTP_SSL’, false); // Use true for SLL connection
The first line is your FTP host name, its usually your domain name but may vary. The second and third are your FTP username and password. And the last line is to user SSL encryption or not.
This is it. Save your wp-config.php without edit any other codes in the page. Then try to upgrade your plugins, you won’t be getting any ftp login prompt again.