The CPU (central processing unit) is an electrical component that acts as the "brain" for your computer. Most video games require certain speeds for the processor to run at in GHz (gigahertz). The games may also specify different speeds for different brands and types of processors. (Tutorial on how to replace your CPU
Your RAM (random access memory) is your computer's "short-term" memory. It stores the current information your game may need to use or manipulate while the game is running. Game specifications normally require an amount of memory in GB (gigabytes). (Tutorial on how to replace your RAM
Your video card (otherwise called a graphics card or GPU) processes and stores graphics information for your game. Most games specifications require models of video cards and video memory required for the game. This is often the most needed upgrade for computers to be able to run higher end games. More-than-likely if you must replace the video card, you will have to replace the PSU as well to meet the new power demands. (Tutorial on how to replace your GPU
Your computers hard drive is the "long-term" storage for the computer. It is where all the program data is stored when the game is running and not running. Most games will notify you in its specifications how much free hard drive space the game will need for an install. (Tutorial on how to replace your HDD
The PSU (power supply) is the component that supplies the power to the entire computer. This will not be labeled on a game specification, but it may still be necessary to upgrade if much of the computer needs to be changed to accommodate the new power requirements. Here
is a great website that allows you to plug in all your computer components and will calculate your power needs. (Tutorial on how to replace your PSU
The sound card is the device the computer uses to output the sound to your speakers. It is often unnecessary to upgrade this, but does reduce a small margin of processing stress on the CPU. (Tutorial on how to replace your Sound Card
The motherboard (aka mainboard) is what all the other components are plugged into and connects everything together. For the purpose of this tutorial we won't be covering replacing the motherboard. This guide is meant to showcase easy upgrades to existing prebuilt computers.