How do you mod your ps2?

The most common way is to install a modchip. This involves opening up the console and soldering wires to the circuit board found inside. This is somewhat complicated and only suggested if you know what you are doing. Keep in mind it's also the cheapest way.

Alternatively, you can buy a pre-modded console, second-hand or from a website. You will pay a premium over a regular PS2 if you buy it new from a website, but used modded ps2s can be found forpretty cheap.