When the Sun has burned all of its hydrogen in its core, it will evolve off the main sequence and rise up the red giant branch.
Later, helium burning will commence, comverting the helium in the core to carbon and oxygen. At this point, the Sun will be a red giant much cooler and bigger than the present day Sun.
After all the helium is burned, the Sun will become a planetary nebula, blowing off its outer layers.
The remnant carbon-oxygen core will become a white dwarf.
