This video gives a wonderful description of simple fish tank cleaning, and remember to return all inhabitants to your aquarium and wait a two of weeks before changing the filter. If the filter is changed at the same time as the other cleaning, an unsafe ammonia spike may occur because all the beneficial bacteria that eliminate the toxins might be removed.  This is vital for your fish tank maintenance.

Clean and replace the filter media entirely. Experts caution that replacing the filter media removes too many of the beneficial bacteria, and triggers a new tank break-in cycle, but most agree that sufficient bacteria inhabit the rocks, plants and gravel.  This prevents the tank from cycling when the filter is replaced. The filter used on your teaching aquarium may determine your approach to  filter cleaning.