Hi my name is ***** ***** I will be the expert working with you today to help and resolve the problem you have posted.
I am sorry to hear that you are having such trouble. I will try my best to help you out and resolve the problem as quick as possible.
You can make the fonts larger from your kindle itself after you install the books.
Let me know the make and model of the ebook reader you are using.
Click here to check the video how to change display settings in kindle.