We often receive requests from players to free up a character name. Customer Support will no longer assist with releasing names. Instead, names will automatically become available if the account that holds the name has remained inactive for the past two expansions.
For example, if an account has been inactive since before the Cataclysm expansion, all names on that account will be made available when the Warlords of Draenor expansion launches.
If you are an active player, there is no need to worry that your character names will be changed, even if you have been playing other characters for a while.