change language of file upload field

I checked your forms and all the file upload fields appear to be in English.  In any case, setting the default language of JotForm to English:

Then replacing the field with a new one, should add the field in English.  You can also set your form to "English" within the form builder:

http://www.jotform.com/help/298-How-to-make-your-forms-multilingual