The amount of replacement of the water in the aquarium depends on several factors, but the general rule is:

Recommendations for changing water:
Small aquarium (up to 100 liters):

It is recommended to change 10-20% of the water once a week.
Large aquarium (over 100 liters):

10-15% of the water can be changed once every two weeks.
An aquarium with many fish or plants:

It may be necessary to change water more frequently (10-20% once a week) to maintain water quality.
An aquarium with calm fish and a small amount of fish:

Water can be changed less frequently, like once a month (20-30%).

tips:
Water tests: It is recommended to check the water quality regularly (chemicals such as ammonia, nitrites and nitrates) to understand if replacement is necessary.
Partial water changes: It is always better to do partial water changes rather than changing all the water at once, as this can stress the fish.
Maintaining the quality of the water is very important for the health of the fish, so it is important to follow the recommendations and perform water changes regularly.

Recommendations for changing water in a large aquarium:
Water change every two weeks:

It is recommended to change 10-15% of the water every two weeks. This helps maintain water quality.
In case of fish overload:

If there are many fish in the aquarium or if the fish are very active, you should increase the frequency to 10-20% water change once a week.
Water quality tests:

Chemical tests of the water must be performed regularly (ammonia, nitrites and nitrates) and the water change plan changed according to the results.

Additional tips:
Avoid a complete water change: it is always better to change part of the water, rather than all of the water at once, so as not to stress the fish.
Using adapted water: make sure that the new water you introduced is in the same conditions (temperature, pH, etc.) to avoid unequivocal changes that could harm the fish.
Maintain consistency and a regular water change pattern to maintain a healthy living environment for your fish!