When you have the book open in Internet Archive, click the "one-page view" button at the bottom right corner of the screen, and then keep zooming in to make the type large and clear.  That one-page view also enables scroll-down. Note the icon with three dots in a circle at the left edge of the book window. Use it to open a screen that allows you to adjust brightness and contrast. You can read Internet Archive books in Adobe Digital Editions if you prefer.  There is guidance here.