Does the character with the name you are deleting have a cool-down period? As in does it need to have not been played on for x amount of time before you can delete it and have the name released to your new character?

The instructions are found here; https://us.battle.net/forums/en/bnet/topic/20761057709

from what I gather the steps are

1) enter chat with character you wish to rename
2) type /rename-character, then type /rename-character confirm
3) wait to receive email. Delete character holding name just before you press confirm with the new name in the email you received

However, the thread you linked is filled with people who were unsuccessful and lost the name they were trying to change to.

This worked, thanks man. The rest of you shut up and learn to actually help ppl instead of trolling. Goes a lot further.