Your pattern may vary, but most Lone Stars are made with strip sets, assembled into the eight (diamond shaped) segments, which when assembled give you your completed star.
To reduce the size simply cut to a smaller dimension evenly. If the pattern says cut strips at 2 1/2, you can cut them smaller equally. What ever size you choose it will come out even due to the design. You really don't need to reduce the pattern on paper because you will be cutting strips and not using a pattern or template. Just substitute the smaller number for the one the pattern calls for.
The pattern will be useful for color layout of strips and how to arrange for finally joining into each diamond segment. This step doesn't care what size it is. As described, this applies to LS patterns assembled from strip sets. Any other way I don't know without seeing the sewing instructions.
I'm hoping you've made a Lone Star before. This is a very challenging pattern to get right the first time around. First off- every seam is sewn on the bias. The cutting has to be precise, and you need command of perfect seam allowances. All seam matching of the diamond shapes is diagonal. You can't nest the intersections, so pin matching, or some other method is required. Then it stretches of course so it's very challenging. And, it's more difficult using smaller parts, so a size reduction increases the difficulty. Each segment must be equal in size and shape, or it won't go together properly.
I just finished two, back to back. The second one was half as hard, and finished twice as nice. I don't mean to "scare" you but the LS benefits from precision joining.
If you haven't done one, give it a go using scraps. I wouldn't take the chance with a $350 kit.