Fitting flue in slate roof

I am fitting a boiler and the flue will go up through the roof, using a roof kit. It is a recently re-done slate roof with the flue going out 3 or 4 rows below the ridge. How do I remove tiles to cut them and fit around the roof flue kit?

You will need what is known as a Slate Ripper which is a long flat implement made of steel with a handle on one end and two hooks for want of a better word on the other end. You slide it up under the slate to be removed and locate the hook around the nails holding the slate and then you yank or hammer the handle downwards to cut through or break the nail thus freeing the slate.This is a slate ripper.........
see this
They are available from most roofing merchants or general builders merchants and should cost you less than £20.

Thanks, sounds a bit like experience is useful for this, maybe I'll get some help on this one!