Here are the steps to change a storage tier (Basic, Mid, High Performance) in VM.
This change is done live without any downtime or service interruption.
1. Login to your vCloud Director.
2. Choose VM need to change.
3. Right-click and select Properties.
4. On General tab, scroll down until you see Storage Policy. Then, select Tier you need.
5. Wait until task finish. Within a minute, you will able to access your VM.