Hi billyfield88 and Welcome to our beginners section!
Good discussion up there. Regular water changes are one of the major secrets to success for beginners. Once you become exerienced there may be different approaches but adding a good water changing habit is a great way to get through the first year or two and experience what a successful tank "feels" like with respect to maintenance and fish and plant health.
In fact a good habit that many of us like to promote is the -weekly- gravel-clean-water-change. It sounds like you understand about the siphoning out part, where you hope to get a lot of the dirtiest water out of the tank. As mentioned there is a pretty wide latitude in return water temperature, but it can't hurt, especially in 50% and larger changes to roughly match the temperatue with your hand. A good way to do this is to use a "catch bucket" when you out-siphon, letting the far end of your siphon hose (assuming you run it out the window to the garden or down the hall to the tub or such) flow into a bucket that subsequently overflows. The catch bucket then has tank water and you can scoop out a cup of that to use at the sink while adjusting the mixing tap to feel the same to your hand as the cup of just-removed tank water does. As said, slightly cooler is better than warmer for the incoming water. Also as said, small changes of less than 50% need less and less worry about incoming temperature.
One interesting thing some people run into with temp is during the summer in air conditioned houses. In my house I sometimes find the air conditioning has made the tank water cooler than the coldest incoming cold water from the water line - this can mean that water refills are warmer and as such I try to make them a smaller percentage in the summer.
"Conditioning" is another safety measure when changing water. It is quite common these days for water authorities to "shock" their pipe systems with extra chlorine or chloramine at times (often during the summer) if the think they may have a bit of excess bacteria in the distant reaches of the system. Since these excess shocks of chlorine products can harm both fish and bacteria, it is a good safety measure to add a high-quality conditioner during water changes. Most of us recommend Seachem Prime for this as it is both very concentrated and also very balanced in its attack on other problems. Conditioner should be dosed at 1.5x to 2x whatever the bottle recommends but as a beginner you should not exceed 2x because your bacterial colonies will still be young. This dose should be calculated for the bucket you are adding if you add by bucket. If you add directly to the tank by hose then you must dose for the entire volume of the tank because the organics in the tank water will use up a lot of the power of the conditioner. Conditioner is cheap insurance. Much of the time is not needed at all technically but that one time it is, it is worth it.
Always perform your various cleaning activities just before the out-siphon. Sponge down your inner tank walls (even if they don't seem to need it) and prune and/or clean your plants if needed. If things get stirred up some, that is the point. If you miss a bunch of weeks then make this activity much smaller and the water change smaller as the temporary stirring up could cause significant toxic spikes for the fish. But if you are regular then the percentage of water change can be based on other things. For instance, those with really soft water will probably want a larger change just so that more minerals (calcium and other good things) are replenished somewhat more. The percentage change an aquarist does is based on a number of factors.
But by far the most important aspect of substrate-clean-water-changes is simply that they get done at all and that they get done regularly. They are a key to being a good aquarist in many cases!
~~waterdrop~~
