Best practice to remove a lun?

What is the best practice to remove an unused lun from qts-5.2.3.3006?
I have little experience with the qnap and would like to remove this unused lun and use those disk resources.
What information would you need to assist me?
Thank you.

Are we talking about a file or block based LUN?

Dolbyman,
Blocked based LUN.

When you remove the LUN, the pool space will be freed up again and then you can grow your volume(s)

Thank you.