To see the current list of running screens:
The first part of the screen's name is its PID. To see the tree of currently running processes spawned from that parent process, run:
or, for a more detailed output,
pstree -a <PID> | less
To reattach to a screen (and detach it if it's already attached elsewhere), run:
screen -rd <PID>
To kill a screen once you've established you no longer need it, you have a couple options. If you're currently attached to the screen, you can simply use Ctrl + a, k, which will kill the screen and all its windows.
Alternatively, if you're not attached to the session, you can use:
screen -wipe <PID>
to kill it and remove it from the list of screens.