Yeah, personally I do weekly 10-15% changes. As Tobigara said you can do it every other week but if it is overstocked then weekly is the best way.
Depending on the size of the tank you might want to either buy or make a "python " water change system. Basically this is a hose with a couple of valves or taps on which you use to drain and refill the water in the tank. If its a large tank it can cut a 30 minute job (which involves heftying around lots of buckets of water) down to a nice a simple 5 minute job (which just involves turning a couple of taps).
Have a look in the DIY section as there is a sticky there on how to make it. Costs around $10-20 to put together and is worth every penny.