Instructions
Click the "Start" menu button, and type "Notepad" into the Search box. Press "Enter" to launch Notepad.
Click "File," then "Open." Navigate to the directory containing the executable file that runs your "Minecraft" server. Double-click the "server.properties" file to open it.
Highlight any text following the "=" sign on the line that begins with "motd." Press "Delete."
Type the text you want to use for the message of the day after the "motd=" value.
Click "File," then "Save." Close Notepad.