The active sessions can be viewed/cleared either from the command line or from the WebGUI.
From the WebGUI:
Go to Monitor > Session Browser to view or clear sessions.
To view the entire session information click on the button shown in the following screenshot:
Now the entire session information can be viewed as shown below:
To clear the session go to Monitor > Session Browser and click on the symbol under the clear column, as shown below:
The session will now be cleared, as shown below:
From the CLI: Use the following command:
> clear session id <id_number>