How do you change file extension for game maker 8.1 so it can be played on kongregate?

To change the file extension for a GameMaker 8.1 project to be compatible with Kongregate, you need to save your game as a .SWF file. In GameMaker, go to the "File" menu, select "Create Executable," and then choose the option to export as Flash. Once exported, ensure the file is named with the .SWF extension, which is the format required for uploading to Kongregate.