Altering Your Print Margins From Photoshop
The big problem people have when trying to change margins in Photoshop is that it is assumed Photoshop behaves like Microsoft Word which leads to some confusion. Unlike Word, Photoshop doesn't use margins, since everything you do is contained on the canvas; this is re-sizable leaving it to the designer to accurately scale and align their image so that it will print correctly.
As I mentioned before though, some projects require you to go to the very edge of the page or at least further than your printing margins seem to allow. How is this when Photoshop seemingly has no margins? There are several options in Photoshop that effect the outcome of a printed document.
There are a couple of things that need to be done before you can freely print on the pages as you please.
Firstly, open the Print dialogue in Photoshop by navigating through 'File > Print' or by pressing the Ctrl + P for PC or Cmd + P for Macs.
From this window it's a lot easier to manipulate and scale the image, so that it fits to your page, without messing with the dimensions of the actual document. This is exceedingly helpful if you need to save the original document for any reason, but need to edit the positioning or scale for print. Often the easiest fix to most printing related headaches is to uncheck the "Center" option, highlighted in the image below. This will allow you to re-size and move your image about the preview page so that it fits to your page as you intend it to.
Another thing worth checking into is the options setup on the 'Page Setup' window which is accessible in the File drop down menu, just above the Print option or by using the Ctrl + Shift + P for PC or Cmd + Shift + P for Mac hot-keys.
In this menu there are options to change the layout and dimensions of the paper. The default is set to standard US Letter paper (8.5in / 11in) with options to change it to A4 or most commonly used sizes.