It won't. (Unless maybe another of the right type of star perfectly enters our system, and they became a close binary system*. But only after ours becomes a white dwarf in muti-billions of years.

Our star will grow to be larger — That's when the sun will become a red giant. It will be so large that it will envelope the inner planets, probably including Earth. Probably because astronomers have noted that as the sun expands, the orbit of the planet's is likely to move farther out from the sun losing mass. As little as just a .15 AU difference may mean earths continued survival.

If earth does get enveloped inside the sun's atmosphere, the Earth will collide with particles of gas. Its orbit will decay, and it will spiral inward. But the Earth will become uninhabitable much sooner than that from a runaway greenhouse effect that is similar to what turned Venus into the terrible hothouse it is today.

After becoming a red giant, then the hydrogen in that outer core will deplete, leaving an abundance of helium. That element will then fuse into heavier elements, like oxygen and carbon, in reactions that don't emit as much energy. Once all the helium disappears, the forces of gravity will take over, and the sun will shrink into a white dwarf. Over a very long time, a white dwarf will cool and its material will begin to crystallize, starting with the core. The star's low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf.

But if it did go supernova while we are still here, radiation, lots and lots of radiation. (credit to AlignedMonkey)

This is not so good for our ozone. Scientists theorize that the Earth's ozone layer would be damaged if a star less than 50 light-years away went supernova. The sun is about 8.3 light-minutes from Earth.

If the Sun went supernova it would have a much more dramatic effect. We would have no ozone. With no ozone, skin-cancer cases would skyrocket. All living things would suffer from severe radiation burns, unless they were underground or in protective suits. Plants would fry, animals would fry...we would all die.

However, if the Sun went supernova the loss of ozone would be the least of our concerns. There would be no escape. On the side of Earth that faced the Sun, the explosion would boil away the surface of the Earth at hundreds of meters per second. People on the night side wouldn’t do much better. Scattered light would heat Earth to lethal temperatures. Scientists estimate that the planet would be roughly 15 times hotter than the surface of the Sun currently is. Far above the boiling point of any known material, and much hotter than any human can withstand (obviously). At best, the Earth would take a few days to vaporize.

*Back to the binary system. A Type Ia supernova (read: "type one-A") is a type of supernova that occurs in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.