It sounds like you are referring to the non-printable margins dictated by the driver.  The driver specifies the non printable margins and those can be different for different media types and media sizes.  When you switch paper type or size, you may see different non printable margins.  Use the Properties button to open the driver and change your media settings or (depending on the printer) margin options in the driver.

Regards,
Mike

Not really sure what you are trying to do; I'm kind of just guessing.  You have placement set to "M" (manual) under the live view which is a specialized placement method that I don't think you want.  Click on that "M", and change placement to IntelliCenter.  Also, the grid lines are just an indication of your current print size which doesn't fill out the printable area of the page.  After setting IntelliCenter placement, go to print sizes in the "Prints" tab and select "Fit to Page".

Again, just guessing but I think that's what you want based on your description as it sounds like you are trying to fill out the entire area of the page that is printable.

Mike