There is no definitive answer to this question. Whenever possible, try not to scale a texture up. But if you must, so long as the texture will be montaged (blended) with an underlying photo, it’s generally okay to scale up to 150 or 200% of the original size. Each texture will behave differently. The real proof is in the pudding. After scaling, double-click the Zoom tool to magnify the image to 100%. If the texture looks good at 100% magnification, it will look good both in print and on screen.