On the official Spock Help/ Faq pages there is one issue that discusses how one can change/ remove the own vote previously done:
Change Your Mind?
In case you entered incorrect information, just click the blue arrow, then "Change Vote," then "Remove Vote." If no one else has already voted on that piece of information, it will be removed from the search result.
But some people could not easily find the "blue arrow" to re-vote/ remove their vote, as it comes from a topic "remove/modify tags... (still un-voted)" on Spock Power Users Group.
So the picture below explains the How-To. Thanks to Kathy Jacobs, Spock Power User and Evangelist, who was the first to answer and to publish this picture.

Keywords: Kathy Jacobs, Spock FAQ, Spock Power Users, Spock.com, Spock