Azure Fortigate VM - Licensing

I have a fortigate vm running in azure which is currently pay-as-you go. I've now purchased a license and want to apply it but apparently this can only be done when the VM is created? What would be the best route to  do this? Config backup, delete VM, redeploy VM, apply license, restore config? Is there a simpler method? Will doing this affect anything else in the resource group? 

Thanks