Oh... oh god yes. This isn't even a question. You should always edit to improve/update/complete/redo/any amount of other reasons. Sure it could change the score of the answer but that is EXACTLY what upvotes and downvotes are for. If that didn't exist, people would be looking at old/outdated/wrong information all the time instead of the newly updated concurrent information that was edited into the post by the person who put in the answer.
Depending on the answer it is also useful to leave the original in tact, add a title and put the new/improved answer above with its own title and date. This way people can see the old way and the new way. And possibly explain what changed to produce the new answer. We have seen a few great answers that have had multiple edits over the years this way and find them far more complete than a rewrite. On rare occasion the old answer might still fit someone's needs, so it's good to have both.*
Heck if a comment is good, and relevant we should edit it into the answer too
*: thanks @KnightHawk, 04/05/2016