Updating Elastic license

Hi, I got a licence key (alphanumeric sequence), but checking the documentation it requires a json file to update the license, I was wandering if you can update the license with this key that I got....or do I need some other data like the one displayed in the documentation.


PUT _license?acknowledge=true
  "licenses": [

How did you get the license key? All licenses I have downloaded from elastic.co have been in the form of JSON documents. Which version are you using?