What resolution should I use when I design my file?
Please design your file at 300 DPI when you design and submit your files. This makes sure that your images remain crisp when we print the files.
To change your image resolution, change that file setting before you design your file. Please note that in most situations increasing the resolution will have no effect on the image if you have already saved the file to a lower resolution.
Lower resolution files still print fine; high resolution simply makes the print look the best it can look.