This article covers Microsoft Azure ASM (Classic) to ARM VNet Migration. The article includes a video demonstration going over the entire process from beginning to end with some troubleshooting in between.
Video:
Steps in the above video covers;
Plan for migration
Install the latest version of Azure PowerShell
Confirm you are Admin or Co-Admin on subscription
Set your subscription and sign up for migration
Confirm available resource in ARM
Migrate virtual machines in a virtual network
Migrate a storage account
Microsoft Azure article covering referencing steps in video