When building or upgrading a computer, it is important to pay attention to the cooling needs of the system. High-end gaming builds will heat up very quickly when gaming, especially if they are being used to their full potential. Overclocking components to get higher performance also generates a lot of heat that needs to be controlled for them to continue to perform at their optimal levels. Additionally, if you are just looking to upgrade, then your older cooling system simply may not be able to handle the newer components. There are a variety of different ways to go about cooling your system. Fans, or air-cooling, is generally the standard and water cooling the high-end and expensive way to go. There are some specific coolers that use a hybrid of water and air cooling to help cool the components. Lastly, when pairing the right cooling system, it is always important to make sure that it is compatible with your other components, such as the CPU and motherboard.
Fans are always included in computer cases, and there are usually mounts for additional fans depending on the size of the case. The fans can come in a variety of sizes, so it is important to know exactly what you need and the trade-offs. Larger fans cool better, but will often create more noise. Fans can also be found for specific components, like fan and heatsink combos for CPUs or graphics cards. These are good options of the fan/heatsink that comes with the CPU, especially if you upgrade the CPU without a fan/heatsink or if you start to run the CPU harder than the standard settings.
Water cooling is very efficient and generally quieter than the spinning fans. However, it is both somewhat cost prohibitive and space prohibitive. Some larger, more expensive cases come with the slots already designed to accommodate water cooling, however smaller or less expensive cases may require some modification to make the water cooling work. However, if you can afford it and your case can accommodate it, then it will efficiently cool off a high-end gaming machine.