How do I fix my ideal standard toilet?

My close coupled ideal standard push button toilet is discharging water into the bowl. On taking the lid off it is running over the overflow. Something needs adjusting what is it and how do I do it ? It is not a normal ball valve it seems to have a tower in the middle which has two 'straws' which operate the small and the big flush and another smaller tower by the side of it which has the float running up and down it. How do I adjust this to stop it running.