Hi Godfrey,
As far as I am aware, the only way to remove the flush buttons and ultimately the lid (if the same model as mine of course,) is to remove the large long flush button first. Ideally you are supposed to push the small button down first, insert a very small screwdriver or similar between the small button and bottom of the larger, crescent shaped one and gently lever the larger one upwards.
If both are stuck down the large one will still need to be lifted out first due to the flanges on the small one. Perhaps you need to stick some thing on top of the large one to lift it up e.g. bluetak or a bit of sticking plaster or tape etc.
Once they have been removed unscrew the fitment with a Phillips screwdriver in the centre and lift out.
The two white nylon posts that support the buttons can be adjusted hightwise by turning anticlockwise.
When re-assembling try it first for height without screwing the 'button holder' down, if still not right it can then by lifted out.
Hope this helps.
Paul,
Nuneaton.
Paul Lathbury.
February 2008