There is no set time /amount for water changes. There are too many variables for each and every tank to give a generic times/amounts of when yo do water changes. Size and number of fish, gallons of water, amount feed, amount of filtration, etc...
Right after your next water change do a Nitrate test. This gives you a starting point. The following water change do a pre water change test. This will give you the amount of nitrates your tank makes in that amout of time. Now it's up to you to decide what amount of nitrates are you comfortable with. Most stick to 20ppm or less. If you do a 50% water change or more you remove 50% of the nitrates.
In my 125gal tank, with a single 12in Amphilophus I did 75% water changes every three days. That kept the Nitrates to 5ppm or below.