I am assuming that by 'habitable' you mean 'in the Circumstellar Habitable Zone of the star,' (aka Green Zone) since that is what is going to change when the sun turns into a Red Giant.
Sol's current CHZ is estimated to range between 0.5AU and 3.0 AU. This wide band is dependent on a lot of things. Earth-like planets can function in the nearer reaches of this, while greenhouse-planets can potentially sustain life further out. (ref)
According to the write up "Can Life develop in the expanded habitable zones around Red Giant Stars?" (ref) They provided a new estimate that says that when Sol enters the Red Giant phase, its new CHZ will range from between 9AU to 22AU. Jupiter is situated an average of 5.2 AU from the sun. This positions it too close to the sun to be within the green band, all the water on Europa would boil off. So no, Europa would not be habitable...too close to the sun.
On the other hand, Saturn orbits the sun at an average distance of 9.6 AU, which plants it firmly in the 'close-range' green band of the new CHZ, which is where Earth-like planets may exist. Titan, one of Saturn's moons, is presently wreathed in an atmosphere of hydrocarbons and has a methane cycle analogous to Earth's water cycle...however, the planet itself is composed of a significant amount of water ice. It would take a lot of work to clean the place up, but once the sun turned into a Red Giant, Titan would be a potential terraforming candidate...if you could get its methane levels under control and stabilize the atmosphere into something humans could breathe.
Do note that this does not mean Titan would be habitable by humans on its own...just that it would be the right temperature for humans to potentially live on. As it is, Titan's atmosphere is not friendly to human lungs, even if it wasn't ludicrously cold. We would have to terraform it first.
The sun would stay in its Red Giant phase for about one Gigayear (a billion years)...so that's how long you'd have to live on Titan.