You can increase the size of your storage disk when your VM instance requires additional storage space. But, You can only resize a storage disk to increase its size, you cannot decrease the size of storage disk. You need to detach the storage from your VM before you Increase the storage.
Open the Storage page, by selecting the Storage menu.
In the Action column, click More then select Detach from Instance.
Click the Confirm button to start the detach storage process.
There will be a notification if the detach storage process is successful "storage has been successfully detached".
On the Storage page in the Action column, click More then select Increase Size.
Select the desired storage size, minimum size 20GB. Then click the Resize Volume button to continue the resizing process or click Cancel if you don't want to change any data.
There will be a notification if the resizing process is successful "storage has been successfully increased".
On the Storage page in the Action column, click More then select Attach to Instance.
Select Instance then click Confirm to continue the process or Cancel to return to the Storage page.
There will be a notification if the attach is successful "storage has been successfully attached".
