Hi,
Since you'll need to update the files on the server, you must have a write access to it.
Usually, FTP is no more activated on servers, because not secure at all. This can be the reason why the access is denied. There should be an ssh access available, so that you can connect on the server and also transfer files to/from it, via the scp command. But
you must know the appropriate credentials (i.e. login/password) or have the keys if ever the password based authentication has been deactivated in favor of the ssh-keys based mechanism.
Anyway you have to be in touch with people who have installed the server and deployed the application on it, since there are the only ones who can provide the above mentioned information.
Regards
Eric