If you want to de-associate your name with stuff you did in the past that's already associated with your name, just stop doing stupid things. People will forget you pretty rapidly if you're not continuously reminding them of it. If it's really bad to the point of possibly interfering with relationships or work, change your real name as well. If you're just trying to get a 'new start' on the internet no longer connected to your old identity or your real life identity, just make a new name, go to new places, and don't sperg out about the exact same niche stuff you did with the old one. In all likelihood as long as you don't continue to do stupid things nobody will ever bother to even try to connect the two identities, and you can go about your life unaffected by your old one.
If you're asking how to delete things from the internet and force everyone to forget about previous clownery immediately, though, you can't.