Free will is the ability to make choices. We do not know exactly what heaven will be like, but the condition of heaven and its greatness does not mean we won't be able to make choices. We are, after all, made in the image of God which includes the ability to freely make choices. Therefore, since the image of God in us is retained in salvation, it is safe to say that we will have the freedom to make choices in heaven as well. Of course, being in the presence of God and his Holiness, and also being in resurrected, glorified bodies, our choices will always be good.