The answer to 'how to kill cockroaches' is to use a combination of DIY methods and professional extermination. For DIY control, you can use bait traps, gel baits, or insecticide sprays in areas where you see cockroaches. These will help eliminate the immediate infestation, but to fully get rid of cockroaches, you'll need to address the root causes like moisture, food sources, and entry points.
If the cockroach problem persists or is severe, it's best to call in a professional pest control company. They have access to more powerful chemicals and treatments that can fully eliminate an infestation. They'll also be able to identify and fix any structural issues that are allowing cockroaches to thrive in your home.