Double click Launch Server.bat
this will create some files. The server will end and ask you to press any key. Press a key to end the server.
A new file called eula.txt will now show. double click this file - change the word false to true. close this file and save changes.
if you have old world data copy this over, copy over any old whitelist or server properties file you want to keep to this new server folder.
Double click Launch Server.bat to run the server as normal.