Problem moving VM to another net.

Hi I am trying to move a VM from the default network to a new network I have created. This page (https://azure.microsoft.com/sv-se/documentation/articles/virtual-networks-move-vm-role-to-subnet/) make it look easy.

But when I run this script I get this error message:

        Get-AzureVM : No default subscription has been designated. Use Select-AzureSubscription -Default <subscriptionName> to
    set the default subscription.
    At C:\temp\net.ps1:1 char:1+ Get-AzureVM –ServiceName abcd-ctx –Name abcd-ctx `
    + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ CategoryInfo          : CloseError: (:) [Get-AzureVM], ApplicationException+ FullyQualifiedErrorId : Microsoft.WindowsAzure.Commands.ServiceManagement.IaaS.GetAzureVMCommand

How do I find the name of the subscription? If this part i needed why was it not on the documentation page? 

I in evaluating mode on azure at present.