SINT - How to change sessionname of running screen instance

Use C-a : sequence, type sessionname myscreen and hit return. And you will get screen instance named myscreen.

screen -ls

There are screens on:
        21084.myscreen  (09/02/2013 09:54:08 AM)        (Detached)
        26413.vmail     (08/26/2013 09:45:35 AM)        (Attached)
        17946.cyberasylum       (08/19/2013 10:21:35 AM)        (Attached)
        6204.comm       (08/17/2013 12:37:48 PM)        (Attached)
4 Sockets in /var/run/screen/S-asfethan.