EDIT: I fixed it, I bought a server, they use Multicraft, so I had to go in there and change the settings there.
You need to change the name in the "server.properties" as well as the folder name. I cant say if it will destroy anything, if you do it this way, but you will keep the world. server.properties got a field for the world-name, so if you rename the folder & the server cant find this world (cuz the folder is renamed!), it will just create a new world.
