Multiple user logon

I keep trying to use ssh shell to access my school's unix server from home and I get this error message:

"This user id is logged on too many times. Please end
some logins to reduce your total number of logins to no
more than 1. Please do so in the next 1 minutes
or you will be logged out by the system."

I know why this happend, I closed ssh without logging off. I type 'who' and I see myself from the previous logon. How do I log the duplicate off?

Try this:

kill -9 -1

It worked, thank you.
I am curious, what did those variables mean?

option -9 kills all the processes
option -1 logs off the user