In most cases, Q class is one of the cheapest seats on the plane. Therefore, it is one of the most restricted fares you can buy. It is usually not upgradable, unless you can get to the gate and there are no other Elites higher than you and there a a couple seats open up front. It is then up to the gate agent to upgrade you or not (they usually will if there are non-Elites on standby so you will free up a coach seat that they can sell at full fare).