how to deactivate license?

[manismanja]

i have 1 license which is can be use to 2 installation....
i already install 1 to my VPS when i want to install another, it said i've used it
i think someone use it (former guy in my office)...and he didnt answer me...
any idea how to revoke it?
so i can use it on my 2 machine....
thanks a lot