Need the name of the pattern or a picture. Much easier to think if have that information.

I'd cut it in half and reduce each half and tape those back together. If it isn't complicated, you can also put a grid of lines on it and draw it to a smaller grid with lines square by square.

You just lay portions of it on a big copy machine at The UPS Store or Kinkos, and keep moving it around until you get it all. Choose the 11" x 17" paper, that will work nicely for you, I think. Since you're going to be using it yourself, I don't think there are any copyright issues. Ask for help if you need it. be sure to enter in that you are reducing the pattern by whatever percentage you determine you want.

I 2nd the cut-it-up-and-copy it theory. If you have a Kinkos or FedEx copy center, they may be able to reduce it for you by a certain percentage...