many times i have noticed that site wit shared hosting do not allow to change settings in php.ini files. one also can not even crate .htaaccess file at all. in such situation one can try following things
ini_set('upload_max_filesize', '10M');
ini_set('post_max_size', '10M');
ini_set('max_input_time', 300);
ini_set('max_execution_time', 300);