Drupal 7 Weform 4 attach file message stays even though correct size file is updated
Have you checked PHP's own maximum upload file size? 

Default in php.ini is usually this: 

; Maximum allowed size for uploaded files.
; http://php.net/upload-max-filesize
upload_max_filesize = 2M


You can check your own site's setting at your sites /admin/reports/status/php