I'm no computer expert, by far, but it should be no problem, as even I can do this.
I have WinXP, and use the MSOffice Picture Manager program, to enlarge, sharpen, define, etc., any types of pictures.
You can also use MSPaint to, although it's a little more complicated.
If you have the same equipment as me, I'll be able to talk you through it. If not, tell me which part(s) of the map you want enlarged, and I'll do it, and e-mail them to you. You can then print them at your pleasure.