Yes, you can easily enlarge (or reduce) the plans however you like, but bear in mind that enlarging the plans from 25-5/8" up to 39-3/8" (approx.) is a ratio of over 150%, and will likely compromise the boat's performance compared with boats that were designed to be One meters in the first place. The most likely problem will be increased displacement, which will call for greater weight. Of course, this can be worked out and adjustments can be made to make the boat sail properly, but it will take some fiddling, and you may never be competitive with a lighter boat. But who really knows for sure? There's really only one way to find out, and that's what makes a developmental class fun! Good luck...

Regards, Bill