There is no simple way to change the virtual network assigned to a virtual machine i Microsoft Azure.
The assignments of locations for virtual machines brings a problem when you need to move a machine to a new network.

The simplest way to do this from the Azure portal is to create a new machine using the following method.

1. Login to your Azure portal and go to the menu for Virtual Machines.

2. Select the machine you want to move and click “Delete”. It is very important that you select “Keep the attached disks. If you don’t select keep the disks you will lose your VM.

3.When the deletion is complete you can go to the Disks tab and verify that the virtual disk no longer is attached to the machine you deleted.

4. Select “NEW” in the bottom left corner and then “From gallery”.

5. Select “My Disks” from the left menu and and check the information to verify that it is the machine you want to move. Press next when you are done.

6. Enter the name of the virtual machine and select the Tier and Size you want. Press next when ready.

7. Select the cloud service for your machine. This is also where you select the new virtual network you want to move to. Select a virtual subnet and press next.

8. Select optional features to be installed and press Finish to complete the move.

9. Verify the move by going to the dashboard of the virtual machine and check that the Internal IP Address matches the virtual network that you want.

Thats it! I hope it helps you like it helped me.