How to delete only an element in a session-php Tutorial

How to delete only one element in a session? Example: session (0 & gt; array (0 & gt; aa, 1 & gt; bb), 1 & gt; array (0 & gt; cc, 1 & gt; dd) now, only aa needs to be deleted. can this be implemented? If unset is not used, the entire sessiondestory will be dropped. ------ solution ------------------ how does unse delete only one element in the session?
For example:
Session (0 => array (0 => 'A', 1 => 'BB'), 1 => array (0 => 'CC ', 1 => 'DD '))
Now, you only need to delete aa. can this be implemented?

If unset is used, the entire session destory will be dropped.

------ Solution --------------------
Unset (session ['username'])
------ Solution --------------------
Session_start ();
Unset ($ _ SESSION [0] [0]);