How is power subverted in Macbeth?
On the whole, I think it's fair to say that power is generally subverted in Macbeth by two means: violence and popular rebellion.
It goes without saying that Macbeth subverts King Duncan's royal power by violently murdering him. However, Macbeth then suffers a similar fate at the end of the play when Macduff kills him in single combat. Thus, it would seem that royal authority is often subverted in the play by violent means. Indeed, even the king isn't safe, as his nobles can easily remove him with violence if they choose to do so.
Along the same lines, popular rebellion effectively subverts Macbeth's tyrannical reign. For example, though Macbeth is theoretically the most powerful man in Scotland, he's no match for the combined forces of Malcolm and Macduff when they rise against him. As such, it seems that the power of kings can also be subverted if the masses rise up against it.
All in all, in Macbeth Shakespeare illustrates the fragility of power and the ways in which it can be subverted. More specifically, he focuses on the ways in which violence and popular rebellion defy and dismantle power structures.