ci_sessions table update user id

I am storing my session data in the ci_session table when using ion auth authentication library. I want to update the data when i am logged in so that i can change the user_id of the currently logged in user therefore switching the logged in user from one user to the other.

The ci_session table has the following fields

id,ip_address,timestamp,data

The data field is holds all data that pertain the session.

The user session data looks like this

Code:

__ci_last_regenerate|i:1491200360;identity|s:15:"[email protected]";email|s:15:"[email protected]";user_id|s:1:"1";old_last_login|s:10:"1491199371";last_check|i:1491200371;message|s:29:"<p>Logged In Successfully</p>";__ci_vars|a:1:{s:7:"message";s:3:"old";}

How can i update data in the data column?