According to the HTML standard, you can not. The only valid values for the method attribute are get and post, corresponding to the GET and POST HTTP methods. <form method="put"> is invalid HTML and will be treated like <form>, i.e. send a GET request.
Instead, many frameworks simply use a POST parameter to tunnel the HTTP method:
<form method="post" ...>
<input type="hidden" name="_method" value="put" />
...
Of course, this requires server-side unwrapping.