how big are they now? photocopier sounds like it would be the cheap and easy solution. If snappy snaps (or whoever is on the high street) cant do it, try an architects office.
I would suggest including a scale on it of known size, so that you can quickly check that it is correct.
I presume you mean enlarging patterns that will be cut out on a bandsaw, not patterns for making a bandsaw.
The easiest way is to put them on a copier with 100% enlargement. You'll have to move the paper around, of course, and make several copies to get the whole thing. Then tape it back together.
Or get some graph paper and transfer it square by square.
But if using the photocopier (or a High Street copy shop) be carefull, you will most probably get get distortions and/or not exactly the amount of enlargement you require (a bitt too small or a bit too large).
+1 for using a scale on the original to check the results, especially if you're paying for the enlargement.