It doesn't cost that much to upgrade to the full package, I have been paying for my hosting at $12.00 a month for the past 2 years. If you purchase it by several months at a time it gets cheaper and cheaper, like a whole year for $99 or 5 years for $299. It is well worth the money, just for all the other things you can do besides remove the bravenet ads.
if it is possible, it probably would not be wise. the advertising is put into a specific place for a specific reason.
as mentioned, you can upgrade to a paid hosting to get rid of the advertising, or you may need to re-do your page to accomodate the advertising in a more pleasing manner.