Hello,
being able to modify the directory via FRP is not satisfactory. You need the correctly set permissions on the Joomla directories.
Joomla ususally runs (should be running) as different user than your FTP account. Most often this is an Apache user name such as apache, www, wwwrun or similar. So, all the named files and directories need to be accessible and writeable by such user.
The easiest to check the correct setting of the permissions is to use the Joomla funciton in menu System / System info / Permisisons.
