Q. Can I change the size of disks when I migrate a VM to Azure?
A. Using Azure Site Recovery (ASR) to migrate VMs to Azure does not allow an alternate size for the disks in Azure. The disks in Azure will be the same size as those on-premises. If you want to change the disk size either resize before migration to Azure or once the disks are in Azure resize them. To resize disks in Azure see FAQ http://windowsitpro.com/azure/how-resize-azure-disk.