40-Character Limit in URL Field for Comments

I'm using Drupal 4.5, and on my site, I allow anonymous comments and offer the option for the poster to leave his or her contact information. Tonight, one person told me the URL field was cutting her URL off and wouldn't allow all the characters. I tested it, and indeed, for those who want to leave their URLs in the field, it allows up to forty characters but cuts it off after that. I tried to see if I could change that setting, but I didn't see anywhere to do it, and I tried searching the forums but didn't find any posts on it, so I'm sorry if this has been addressed before. How can I up the limit? Thanks a lot.