Unvoting is generally not a good idea, it costs you 1 Ark to unvote and another 1 Ark to vote for a new delegate. Just send your Ark to a new address in your wallet for 0.1 Ark and vote on the new address for the new deleagte with 1 Ark, in sum 1.1 Ark and not 2 Ark. In the case you want back to the first delegate just send your Ark to the first wallet for 0.1 Ark, you don't have to unvote/vote again.