meganbmoore | tags question

Does anyone know how to merge tags without going through and manually changing the tag on every single entry? I have, combined, about a hundred entries left to go through and change from "manga 2" and "dorama 2" to just "manga" and "dorama," and even though I've already done about twice as much in tag changing already...I'd really love it if there were a way to spare myself those few hours...