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You have 3 **Default** *worlds : world, world_nether and world_the_end*, they are all linked together...
To make a new uploaded world *Default* : **Stop** server then go to **Server Properties** then in **Level Name**.. *Change* that name to the new uploaded worlds name.. once changed and saved, **restart** server, it will then create new *Nether* and *End worlds*, all new worlds will be *linked* to each other, you can then **delete** the other 3 worlds, i.e *world, world_nether and world_the_end*.... (on a side note all playerdata saved in default *world*, in playerdata folder)..