Way, way to the left at the top is a minus sign, % for size of image, and then a plus. Is that what you are looking for? About in the middle is a maginifying glass, that also changes the size of what appears on the screen. The actual printing would depend on the printer settings and that would be set in the properties for the printer.
I think I know what you mean - the dpi settings for saving a file? If so, go to Distiller (in Acrobat, it's under Tools, then click Disttiler), Setting, Job Option. Under the General tab, there's a dpi resolution setting, then under the Compression tab, there's more dpi settings. You'll probably just have to play with the settings to find out what works best for you.