Spam, Spam, Spam.....

Hello, I am in need of a great amount of help. Please bear with my, because I'm quite new to this whole process. I use yahoo business as my server and uploaded this guestbook at their advice. While I like it, I can't seem to stop the spam from coming in. I have version 2.3.1 and am not sure how to update without erasing my entries. Can anybody please help me in laymen terms. Thank you very much.

Download 2.4.3. Open your config.inc.php file from your 2.3.1 installation and copy the database information into the config.inc.php file of 2.4.3. Upload new guestbook and visit misc/update_db.php in your web browser.