Need help with my form with duplicate file and resetting form
As described in the docs file_save_upload
file_save_upload($form_field_name, $validators = array(), 
$destination = FALSE, $replace = FILE_EXISTS_RENAME)

the last parameter $replace

$replace: Replace behavior when the destination file already exists:
FILE_EXISTS_REPLACE: Replace the existing file.
FILE_EXISTS_RENAME: Append _{incrementing number} until the filename is unique.
FILE_EXISTS_ERROR: Do nothing and return FALSE.