If you choose the Ruler tool, hold down the Shift key to draw a straight vertical line, the length of the line you draw (with the Ruler set to inches) will appear in the sections of the Info panel shown above. From that information, calculate the percent of enlargement or reduction (simple arithmatic) required to match the original art and in Image > Image Size enter the information as a Percent, an option offered in Image > Image Size here:
One last reminder, Wally: a change in the file's image size may impact on the image's quality.