Azure allows you to download a template for a running VM and deploy it using the command line

This is useful if you want to modify the template and deploy slightly different values. For example you cannot deploy a Windows VM with an OS disk greater than 126GB, in order to do so you must add something like this to the template and deploy via the command line(described here):

  "dataDisks": [
      {
          "diskSizeGB": 500,
          "lun": 0,
          "createOption": "Empty"
      }
  ]

I would like to increase the OS disk size on my VMs managed by the Azure VM Agents Plugin and this is the only way I can see to do it for the time being, unless you add a feature to the plugin to set the OS disk size (I am planning to open a feature request or improvement issue for this request as well. Edit: JENKINS-51528 added.)