Why don't you try
Changing the dinosaurs for a different sprite
Select a sprite then select a costume (tab next to code)
You will have to do this for each sprite.
Make the dinosaurs roar
Add a sound to be played when the sprite is clicked.
(keep the sound short to keep the game fast).
Add extra dinosaurs
First make some new 'holes' by editing the backdrop.
Then right click on one of the dinosaur sprites and select duplicate.