It's hard to say on the water change without knowing your levels. An API freshwater master test kit is sold at any fish/pet store for maybe $15. You'll want to test your levels & that'll help to know how often or how much of a change to do as they can easily be poisoned from ammonia (especially in new tanks), nitrates, & nitrites.
. I think without a kit, I'd let it be for another few days. Any time changing or adding water, be sure to use the solution & do smaller changes to keep from throwing ph balance off. More often if needed but strongly suggest a kit. That's where your answer is.