Hi there Nancy. My name is***** am a computer professional with over 15 years of experience with both Mac and Windows computers, phones, tablets, and printers. It would be my pleasure to assist you with this. May I ask please what type of ereader you have? Is this is a Nook or a Kindle?
I realize that 240Mb may sound like a lot of memory but it actually isn't. You definitely need to remove some of the books that you have read from your device. You can archive them in your account on either Barnes and Noble or Amazon, depending on which device you have. Once you've let me know whether it is a Kindle or a Nook, I can provide you with step by step instructions for doing this.