Agree with the others, with one additional caveat. Understand that large, massive water changes all in one shot, may not be safe with your tap water, and your fish. Lots of things need to be considered before one begins doing massive water changes.
In my tanks, with my fish, my biofiltration, my tank parameters, my tap water, and my water conditioner - I can personally get away with that, year round.
You on the other hand might not.
When it comes to water changes, one size does not fit all.