No you cant. That's the beauty of steem blockchain.. Whatever you do in steemit or anyother apps or site based on steem blockchain is stored there forever.. You can edit something but the original along with the edit will also be stored there. You can see them with any steem blockchain explorer.

one thing you must have noticed that you don't have to put unnecessary personal information when using steem. But every thing you do on steemit is clear as crystal. Including every transaction you have ever made and will make.. This is to keep the community excluded of deciet or falsehood.. No one can manipulate anything here..

If you think how is this secure enough for me. Well I don't see any of the limited amount of personal information I have used such as my phone number and my email to be displayed in my account...Information about All of the transaction I ever did is available to anyone but not anything that could come back to bite me. That is the reason why steem is so much powerful along with everyother blockchain.