Designs cannot be made larger than the original size purchased, but can be scaled smaller if you desire. Your print/manufacturing shops can do this for you or you can rescale the item yourself. Her is instructions below for how to do this yourself.
Mac Users: Open the seamless file in the application: PREVIEW
Chose>Tools>Adjust Size then enter a smaller value in inches and make sure to save it as a NEW file on your computer so you don't save over the original.
Windows: Open the Photos App
Double click the image file you want to resize to open it in photos. Once opened click the three dots in the top right corner, then click "Resize." A small pop up will appear, offering you a three preset size for the picture. Select "Define Custom Dimensions" and rescale as you wish. Make sure to save a COPY of the design so that you keep your original the original scale.