@Valerie Winner - Only the owner/creator of the board can delete it. If you are a Team Admin of the team/space where the boards reside, you can remove the user from your team at which point you can chose to remove the user and delete their content.

Thank you!
But if I just don’t want to see their boards?
Can I move out the team if I’m not an Admin?
Or can I contact the owners there, because I don’t remember who they are in person 

Hi @Valerie Winner,

Let me step in for a moment. If you just want to hide the boards created by other members of your team, you can apply sorting to the content on your dashboard and select the Owner by me option:

This should do the trick!