Quick Feed:
If you want to change Azure VM instance Size, use the following Powershell method.
$vm = Get-AzureRmVM -ResourceGroupName “yourresourcegroupname” -Name “YourAzureVMName”
$vm.HardwareProfile.VmSize = “Standard_A2”
Update-AzureRmVm -ResourceGroupName “yourresourcegroupname” -VM $vm