I'm very tired of being alive, it's messy and ugly and overwhelming, I just have no insterest in it. How can I change my mind when everything seems meaningless?

You've already accomplished a good first step, which is recognizing that you want a change and reaching out. One thing that has helped me, personally, to gain a more positive outlook on life is to create a "love list" of little, seemingly insignificant things that bring me joy. It started off as a brainstorm, but now every time I see a rainbow, hear a bird sing, or notice a funny shaped cloud, I quick add it to the list in my notes app. It's helped me to actively appreciate the little things that make me happy, and when I feel like life is meaningless and depressing, I take a look at my growing list of things I love and remember that the world is a beautiful place full of amazing things, and that I don't always feel this overwhelmed.

Well.. there are times I feel the same way. But what brings me back to surface is MY PURPOSE. Deep down I know why I exist and what keeps me alive. This can bring a meaning to your life and show the bigger picture of your existence. This is what brings you joy and creates happiness. Purpose can be really powerful and it also sets the direction. This comes in handy specially when you are down. Its like a compass that sets the way. Its not easy to craft your purpose at once. There are many material around how to create your own space.