Deleting a message or conversation??

How do you go about deleting a message or conversation. 
Can you block someone who is bothering you. (no one is bothering me, I'm just asking)
Thanks

Mark

You cannot delete conversations and messages at the moment. Although cancelling your account will destroy those messages from the server, including on the recipient's side.

You can block someone who is bothering you by clicking the 'Block' button under 'Add Friend' on their profile page.

Thanks Mark!!  I really hope they will make it possible to delete in future.