I don't know if people can change their sexuality, but I don't think that's the question that really matters in regard to spending eternity in heaven.
The question as I see it is whether we strive to become more like Christ by not acting upon our sinful desires. We're all sinful and we always will be regardless of the specific ways we are sinful. Homosexuals can choose to live chaste lives. This honors God more than heterosexuals who don't honor marriage as God intended it.