The reason humans forget things is because we are constantly learning new things. If older information is constantly reused, it is considered 'important' and we keep it around. Anything that doesn't matter gets pushed aside to make way for new things. Most of the time, we'll consider those things forgotten, yet we sometimes find that, under the right circumstances, remembering these is still possible.
The internet works essentially the same way. If the only mention of you on the web is that time you got arrested for vandalism in high school, you can fix that the same way you'd fix a relationship with a high school classmate who only remembered that fact. Show them that you've changed by creating new content that paints you in a more positive light. Maintaining your public image is an important skill, and for certain positions, it even makes sense for employers to screen for it.