You can change your writing environment any way you want to suit your liking. Zoom in to get larger text, shrink the width using the ruler, increasing the line height, etc. When you have a setting you like, set this as the default in Preferences and then convert all your text to this format
The only thing I’d add to Lunk’s suggestions is that once you know the maximum text width you prefer, set your ruler back to maximum and use Scrivener->Appearance ->Main Editor->Options to control the maximum editor width and displayed margins. (It’s implied but not actually stated in Lunk’s directions, and I personally would find his directions rather confusing. Since you seem to be doing fine, my clarification is for anyone else who might read this and be as confused as I.)
Must admit that since this is my first Scrivener canoe trip I am still apprehensive about what I will be facing with the publishing formatting and the usual last minute tweaking.