How do I convert toilet flush from handle to push button?

The siphon in the toilet cistern has already been replaced once but the same problem is recurring. However hard you depress the handle there's little or no resistance and sometimes more than 1 flush is needed. It's a Shires toilet, approximately 19 years old. As the bathroom suite is coloured, replacement of the toilet is not a preferred option. Can it be converted from lever action to push button & how difficult would this be?