Change enough water to get you ammonia and nitrite under 0.25.
I was changing 50% , waiting an hour, changing 50%, and again after another hour. I was doing this every day, and by the next morning my levels will be sky high.
I have heard that changing the water can stress the fish, but mine seemed quite happy with it, and seemed very interested in the plastic jug I use for scooping water out
Even if the change does stress the fish out, it'll still be less than the stress they'll feel with high ammonia/nitrite.