Changing page margins for an entire document

[spruce_xent]

Hi, I've tried to search this in "search" here but my specific problem eludes me, even though i guess it's fairly simple.
I would like to change page margins for an entire document. When i go to page in the format drop down menu it seems to only change for the page I'm currently on and not for the entire document, I have tried selecting all and also changing the margins on the left hand side where there is a measuring ruler, but again it works page at a time and not for the entire document. I know the answer is fairly simple... i just don't know it.

If anyone would care to illuminate me
Much appreciated....

[RoryOF]

Use /Format /styles and Formatting; press 4th icon from left to show Page Styles; use the dropdown on the bottom bar of the Styles and Formating Window to select Applied Styles. This will now show you the actual Page Styles in use. Right click on each such style, choose Modify, and on the Page tab of the window that pops up set the margins you require.

Edit: In a well formatted document there ought be only a few page styles - typically five or six; so alteration of the margins is not a major task.