There are currently two downvotes and one upvote on your question. This could have happened if someone removed their downvote, or if someone flipped their downvote into an upvote.
Usually, votes are locked in and cannot be changed at will, except for a grace period after casting the vote, or after the post was edited. That is supposed to encourage ...
StackExchange uses voting system to make good answers go all way up and bad ones all way down, not to give rewards and reputations to people. (And a reputation system is perhaps a way to rate users as well as give them permissions based on their reps)
Upvoting/Downvoting means this vote is useful/not useful