You need to add a second parameter containing the product hash (see https://github.com/mex/rent-it-client/blob/master/lib/request.js#L29).

Example of this:
```
request.put('ProductService.svc/products/' + req.params.id, {
  name: 'Hammer',
  description: '...time!'
}, function(err, payload) {
  // Do something...
});
```