how do I reduce the top margin in my task page

[Redwine]

I have tried reducing the margin in page set-up but it will only allow me to
go as low as 0.7 cm. Below that it tells me to margin is too small. Yet still
20% of the top of the page is blank. I use A5 size paper setting as the
printed document goes in to my A5 Filofax.