Minecraft Server no longer works?

Alright dude first thing is first, i get that you are tryin to change yo world but man… It aint possible coz once you create a server assigned to a world you can't just change it! So right now i don't think there's anything possible right now but then just reverting to your old world sorry about this bro…

In the Server.properties file, make sure you're also specifying a new world name. If you'd like the re-use the name of your existing world, you'll need to either rename the folder of that world or else move it to another directory.

As you've changed the level type field, make sure what you've entered is actually valid. There are only four level types you can define for map generation and this is only valid for that world. Changing it later won't regenerate the current map.
- DEFAULT - Standard world with hills, valleys, water, etc.
- FLAT - A flat world with no features, meant for building.
- LARGEBIOMES - Same as default but all biomes are larger.
- AMPLIFIED - Same as default but world-generation height limit is increased.
Source: http://minecraft.gamepedia.com/...properties