I have one account and I've got a merged account, where I play, but I want to merge the one with the another account so I could convert characters. It is possible to have one battle.net account with more wow accounts?
Yep. Once you have merged multiple WoW accounts into the same battle.net account then you have a drop-down menu on the login screen for which WoW account associated to the battle.net account that you wish to play.