You don’t have to completely change the water. Only 30-60% and moving your fish back and forth could stress them. Especially if your doing water changes with a fish in cycle. You should be changing the water everyday or every other day to keep the ammonia down. Ask your lfs if they can give you some cycled media even if it costs you 5 bucks. Put that in the filter . It will kick start the cycle. Also buy a master test kit if it haven’t already and test the water daily. And when I do water changes I fill my buckets slowly and I drop the thermometer from my tank in there. And I try and get it within -2/+2 degrees it will balance out with the other 50 percent of the water