You cannot simply just delete anything. Once you publish anything to a relay, such as a note or account, it's there to stay.

You can *request* that a note or account be removed from relays, and some will accept the removal request. However, most won't. And even though some relays will remove the data, it will still remain on the relays that didn't.

And even the relays that will remove the data, I'm pretty sure that they will just eventually download the information again if it gets observed by a relay that still has the data.

Just be careful what relays you connect to, and/or what you are publishing.