I have a bunch of old WordPress installs that I manage. I have been updating them from the command line and updating plug-ins by dragging them from my desktop to the plugins folder using Cyberduck. There is an easier way but it requires a few tweaks to your install.
First you need to change the ownership of each file to www-data. I also change the group to the users group.
sudo chown -R www-data .
sudo chgrp -R user .Then you need to add a line to the wp-config.php file. I added it to the last line of the file.
/* Sets up direct method for updating without FTP */
define('FS_METHOD','direct'); Now anyone with a dashboard login can update the site.