Hi @KatherineCraig,
If you convert the quizzes to New Quizzes, you'll be able to set the total quiz points independently of the quiz questions, making the task of changing total points much easier. For example, you could have a quiz with 10 1-point questions, but have it count for only 5 points in the course (Canvas calculates a percentage score based on the question points then scales it according to the total quiz points). The points the quiz counts for in the course are set in the quiz details area, which the question points are in the build area. I hope this makes sense.
If you want to stay with classic quizzes, I don't know of a way to adjust the points without editing each individual question (unless you're randomly drawing from an item bank, which might have one points option per quiz).
-Chris