To update channel entry nGen File Fields to Native Files after upgrade process:
UPDATE exp_channel_data
SET field_id_XX = CONCAT('{filedir_YY}', field_id_XX)
WHERE field_id_XX != ''
AND field_id_XX NOT LIKE '{filedir_%'
XX = The field ID to update ( same as ID in control panel, a column name in the SQL table ) YY = The id of the file upload directory form the File Manager