1. Just delete the "world" folder already on your server, then rename your current map directory as "world" and upload it.
2. If you want to keep your current world folder for later, just simply rename it to something else. Then rename the map you want to upload as "world" and upload it.
3. If you don't want to delete or rename your current "world" folder and just want to run off your own custom folder name, then just upload it as is. But if you do this, you will have to enter the name of your world in the game panel, hit save and restart. So if you upload the directory as "World2", then you will need to enter "World2" in the game panel world section so it reads your map from that directory. Here is where you enter it:

**Note - If you are uploading this world but wish to add it to the server as an extra world through a plugin such as MultiVerse then you do not need to change the World box on the control panel. This box should always be listed with your *main* loaded world when using multiple worlds.
When using a plugin to load multiple worlds you can simply import the world you uploaded through that plugins relevant commands (For example '/mv import [worldname] normal' to import an overworld world through MultiVerse).
When using a plugin to load multiple worlds you can simply import the world you uploaded through that plugins relevant commands (For example '/mv import [worldname] normal' to import an overworld world through MultiVerse).