If by "devote" you mean "unvote" or to remove your vote, then you can just simply click on the upvote button again. Once you click on the upvote button again, a pop-up will appear to confirm your unvote. Just click on the "OK" button and your vote will be remove.
However if you mean by "devote a post" here like give all the post payouts to other users, then you can set them as "Beneficiaries". One way to do this is through SteemPeak.com. Just input the username of the one who you want to share a percent of the post payout and how much in % will that person get.
For example if you set it at 20%, then that person will get 20% of the payout which will be paid in Steem Power.