Open the image in an image editing software such as Photoshop, GIMP, or Canva.
Convert the image to grayscale by desaturating it. In Photoshop, you can do this by selecting Image > Adjustments > Desaturate. In GIMP, you can select Colors > Desaturate. In Canva, select the image, click on Edit, then Adjustments, and then Grayscale.
Adjust the levels of the image to increase contrast. In Photoshop, you can do this by selecting Image > Adjustments > Levels. In the Levels dialog box, you'll see a histogram that represents the distribution of tones in the image. You can adjust the black, white, and gray points of the histogram to increase contrast. Drag the black slider to the right to darken the darkest areas of the image, and drag the white slider to the left to lighten the lightest areas. You can also adjust the gray slider to modify the midtones. In GIMP, you can select Colors > Levels to access similar options.
You can also use the Curves tool to adjust contrast. In Photoshop, you can select Image > Adjustments > Curves. In the Curves dialog box, you can create a curve that increases contrast by making the darks darker and the lights lighter. Click on the center of the curve and drag it upward to increase contrast.
Experiment with different levels and curves adjustments until you achieve the desired level of contrast. You may also want to adjust the brightness and contrast of the image to achieve the desired effect.
If you don't have access to image editing software, you can also use online tools to convert your image to grayscale and adjust contrast. Some popular options include Pixlr, Lunapic, and Befunky. Simply upload your image to the tool, select the grayscale option, and then adjust contrast using the available tools.