How do I beat king's indian? I'm having a hard time.

You can't really use stonewall as a system. As a general rule of thumb only play the stonewall if black commits to playing d7-d5 and weakening the e5 square.

The point of the setup d4, e3, f4 is really to create an irongrip on the e5 square and it would be kind of useless if black could just conquer that square himself by doing something like this:

seeing the KI coming , nobody is going to play F4.

conzipe is right! the colle can be used as a system and you can use the stonewall sometimes as well as the torre attack as well as the queens gambit which nakamura plays to to this day. study the colle system and youll develop better practices and move and might even develop a repertoire using d4. if not go back to e4. good luck