If you look you will see a small cross head screw going into the side of the primer lever, you need to undo it, not all the way as this holds the primer handle in place. Then look at the carb the when you pull the primer it operates a arm that moves down onto the carb and pushes a little blue knob down, this is the primer its self.....
So... get your hands in and push that lever down onto the carb and give a sharp pull on the knob its self and it should come out. Not forgetting you need to remove the retaining clip from the back of the knob itself first.
If all that makes sense????!!!!!