Sanyo MM-8300

Many of the sites that worked on my old, free, outdated Nokia come up terribly on my new, expensive Sanyo, most notably Yahoo mail. I have been 'round & 'round with trying to upgrade IE, "return to the version of Yahoo supported by my current IE version," etc., but it's one big, ineffective circle of doom. How do I update IE on this phone so the sites work properly? Thanks for any suggestions!