How can I logout an open remote SSH session ?
Run tty on your current session, to find out on which tty you are working, so you do not log yourself out from current session
[firstname.lastname@example.org ~] # tty
Run w to show you current users and associated pseudo-terminals(tty).
Assuming that you are logged twice and there one other users on your ssh server logged in from pts/1 ,
Your previous ssh session will be on pts/0 and current on pts/2.
To ditch the session on pts/0 simply kill processes that are associated to it with
# pkill -9 -t pts/0