How to fix faulty brakes in an Audi A4?

I have noticed that my brakes in my Audi A4 have been feeling spongy and not as responsive as before. How can I fix this issue myself without having to go to a mechanic?

The first thing you should do is check your brake fluid levels. If they are low, you can top it up to the correct level and see if that improves the brakes' performance. If not, there might be a problem with the brake lines or calipers that will require professional attention.