I can't make myself an op on my minecraft hamachi server?

After redownloading hamachi and the rest of the server files after i re-bought minecraft
i tried to op myself for my server and when i saved it and then joined my server, it wouldn't allow me to use any op commands.
i don't know what's going on but yeah.
it's the minecraft 1.7.9 server download, and the minecraft is the same.