Can be cut as hard as you like in mid winter - not sure what the weather's like with you where you are, but if its still winter, take off as much as you like. You won't get flowers this year, but should get some next year and certainly the year after. In following years, prune immediately after flowering.
Give the cut back shrub a good general purpose feed as the growing season begins.

OK but where on the plants do I cut?

Wherever you want the final height to be.

Thank you very much. Any suggestions on my third question?

I've posted under your third question already...