If you are adding a new single image component to the page OR have clicked the Edit button above a single image then you should get the screen below. Click the Browse button that the red arrow is pointing to. That will open a window to select files from your computer. Scroll down this page to see an example of that.
After clicking the Browse button you should get a small window like the one shown below. Find the image you want to upload on your computer by clicking through the various file storage areas available as indicated by the green arrow. Then when you find the file, click on it and the file name should be shown in the box indicated by the blue arrow. Then click the Open button that is indicated by the purple arrow. The image will then be loaded into the setup page that was shown above. You can then resize or crop the image as needed by clicking the Resize/Tools button that will appear above the image.