Reclaim disk space after deleting VHD

Hello,

There is a case where a Hyper-V cluster is installed. We created an new LUN ,than we moved one VHD from the existing LUN to the new one but the free space is still the same on the first LUN. ( example : if the free Space is 1.5 TB we deleted a 0,5 TB the free space should be 2TB but it's still 1.5TB)

How can reclaim the deleted space??

What could be problem? and what the best practices for creating LUNs?

Regards,