If you don’t have a calibration tool the best you can do is use a site like this:
http://www.lagom.nl/lcd-test/
A couple of notes on using Lagom. It’s been around for quite some time now and with the emergence of ever higher resolution displays over the last 10 or so years Windows and browsers are scaling images now, so you might have to download the images and view them in original size using Photo Viewer or MS paint (select in menu). This is particularly important for images found in the Gamma and Gradient tests, as they must be viewed at 1:1, pixel for pixel on your display to work correctly. Also note that the tests should be done in the order they are presented on the website because later settings depend on earlier ones when adjusting your display. Some of the tests are informational and not really needed for calibration. The tests I primarily use are Contrast, Gamma, Black Level, White Saturation, and Gradient.