Yes you can. Often in leakage sensitive spots higher voltage ratings are used because this means thicker dielectricum hence less leakage current. Modern electrolytics are a lot better in most aspects than older products, so there´s no problem to be expected.
But sometimes in production runs nobody cared about the necessary voltage rating. Buying parts cheap in huge numbers ruled out other factors. That could have been another reason for these caps being 40V, simply because they were available cheap and in huge number in the storage.
I bet you´re talking about C7,10,17,20. I´d increase them in capacity anyway. This will lower phaseshift in the LF area.