You can enlarge your family tree by changing the number of page that you print out for the tree. For instance, for a "long" family tree, you could set the Width to 16 pages and the Height to 2 pages. Or, for a tall family tree, set the Width to 8 pages and the Height to 8 pages. I had to experiment a bit before I found numbers that worked for me.
Once you download the PDF, you'll have to print them out and tape them together, and you'll probably want a paper cutter to cut off the edges of two of the sides (like top and right) so that you can tape the pieces together without a empty space where the margin is.
Alternatively, there are companies that will print out your family tree for you from your GEDCOM file. This resource lists a few of them toward the bottom of the page. Note that your GEDCOM file doesn't include pictures.
I actually purchased Family Tree Maker just to use their charts. I work in FamilyEcho and then export my GEDCOM file and import it into Family Tree Maker. They have an option where you can print out your whole family tree (subject to the normal limit of how much of a tree you can realistically display at a time) as one large PDF (instead of splitting it into multiple pages. But there is a limit to PDFs of a maximum width of 200 inches (about 17 feet), so there are some compromises there as well.