You need to change the screen resolution
I see this advice given frequently, but it is not a good solution.
Modern displays are designed to be used at their native resolution, and do not perform well at other resolutions.
Images will look less sharp, at 1:1 the difference in sharpness can be quite dramatic, which could lead the user to oversharpen.
There are really only two solutions - either run old software on a standard resolution monitor, or use the latest versions that are designed to run on HiDpi/Retina displays. These displays should have a warning sticker on the box (like on cigarette packs), a lot of users have no idea what they're in for.