Hi Santi,
as I have said, there is no update functionality. If you want to update templates you got to delete them first.
Regarding the templates that don't appear I would ask you if the template class exists? If the templates are of a certain class that does not exist you have to create that class first (e.g.
insert into mc_template_class values ('<name of class like Z_PF>', NULL, 'PAR_<parname1>|PAR_<parname2>|...', '', (SELECT mcPackageID FROM mc_package where mcDisplayName = '<yourPackageName like com.sap.core>'))
Regarding the picture, it looks like the service user that the J2EE is running with (sap<SID>) does not have access to that folder. Either way, that is a local path and that reference wont work in the email on the clients desktop at all anyway. You should upload that picture somewhere on a web server and refer to it via HTTP URL as shown in my example.
Regards
Norman