When you have your documents folder open, look at the top of the window and you'll see a set of icons. There are four close together, click the first one to go into thumbnail view. Now at the bottom right of the window there will be a slider. You can drag the slider to the right to make everything larger.
If you prefer to stay in list view (which is probably what you've been looking at) you can make things a little larger: go to the View menu and click a View Options. There should be a drop down for text size which will increase the text and icon size by a few points - you should set it to maximum.
You can also decrease the resolution of the whole screen from the Displays section of System Preferences (from the Apple menu at the top left)
There are also zoom options available in the Universal Access pane of System Preferences but see how you do with the above first.
Matt