'Updates an OS image that in your image repository.
image_name:
The name of the image to update.
label:
Specifies the friendly name of the image to be updated. You cannot
use this operation to update images provided by the Windows Azure
platform.
media_link:
Specifies the location of the blob in Windows Azure blob store
where the media for the image is located. The blob location must
belong to a storage account in the subscription specified by the
<subscription-id> value in the operation call. Example:
http://example.blob.core.windows.net/disks/mydisk.vhd
name:
Specifies a name for the OS image that Windows Azure uses to
identify the image when creating one or more VM Roles.
os:
The operating system type of the OS image. Possible values are:
Linux, Windows'

def update_os_image(self, image_name, label, media_link, name, os):

    _validate_not_none('image_name', image_name)
    _validate_not_none('label', label)
    _validate_not_none('media_link', media_link)
    _validate_not_none('name', name)
    _validate_not_none('os', os)
    return self._perform_put(self._get_image_path(image_name), _XmlSerializer.os_image_to_xml(label, media_link, name, os), async=True)
