When you try to upvote the guide, there should be a tab that shows up at the bottom, no?
If you click the green upvote button at the top of the guide (next to the downvote), the new vote should go through and remove your earlier vote.
If you click the green upvote button at the top of the guide (next to the downvote), the new vote should go through and remove your earlier vote.

Thanks to jhoijhoi for the sig!
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