That's kind of impossible. Which is the point of the immutable ledger. Once you post something, it stays on the chain, forever.
Delete posts from Memo.
You can't remove something from the blockchain, but you can take it off of Memo.
That would require the server hosting memo.cash to keep track of user data. AFAIK, at the moment they're just querying the ledger for whatever data they need, and serve it as is.
