Server API Connect PUT based on GET values

I have successfully connected the Server API to a datasource and can query all records and list them in a repeat.

I authenticate server side and call a URL
e.g. http://my.webservice/test/{123456789}/accountlist

This then lists all customers and the response contains the name, limit etc.

"$resources": [
    {
      "$url": "http://my.webservice/test/{123456789}/accountrecord(1dfc-4dba-8cac)",
      "$uid": "1dfc-4dba-8cac",
      "active": true,
      "name": "ABC Ltd",
      "credit": "1000",
}]

I need to perform a PUT method to update the desired selected record.

The URL to post to is the $url value in the response or it’s always http://my.webservice/test/{123456789}/accountrecord with $uid enclosed in brackets.

Any pointers would be really appreciated.

Thanks