FTP / File Manager cannot edit file

[maddunr]

I have tried this using File Manager (in Plesk) and other FTP clients, but my FTP user doesnt seem to have write access (or that's what I think it is). Here's the error I received when using File Manager in Plesk:

Unable to edit file /httpdocs/new/mambots/editors/htmlarea3_xtd/popups/ImageManager/config.inc.php: filemng cp failed: cp: cannot create regular file `/home/httpd/vhosts/domain.com/httpdocs/new/mambots/editors/htmlarea3_xtd/popups/ImageManager/config.inc.php': Permission denied filemng: Error occured during /bin/cp command.

Can someone pls help?