The Sun is slowly growing more and more luminous.
Earth will become uninhabitable to organisms other than thermophilic bacteria in the almost-boiling oceans and continents will be scorched down into desert wastelands. Part of the oceans will subdue to the mantle, and part will evaporate turning the atmosphere into a hellish moist-greenhouse sauna. The surviving surface water would be very near to boiling.
By 2.8 billion years from now, the surface temperature of the Earth will have reached 422 K (149 °C; 300 °F), even at the poles. At this point, any remaining life will be extinguished due to extreme conditions.
After that, Earth will be "venusified" with the destruction of its water vapor.
Then, as the Sun enters the red giant phase, it will swallow Mercury and Venus and possibly also the Earth. Even if Earth escapes being swallowed, it would be scorched and burned to a crisp beyond recognition long before that, having its surface melted into a lava ocean. It is also possibly that Earth loses the Moon if it escapes.
After the red giant phase, the Sun shrinks down and becomes a small white dwarf shedding a stellar nebula.
Now the question:
We, humans, have a lot of time (millions of years at least) to prepare for that, but nature won't wait for us.
How could we progressively move Earth to a larger orbit and prevent its natural fate until the end of the red giant phase¹ while still having trees, flowers and animals happily living² in the fields and oceans of the planet which we call home?
¹ Surviving the shrinking after the red giant phase would be "just" reversing the orbit enlargement. But surviving being enshrouded in the planetary nebula is topic for another question, so I will leave that out of this one.
² Don't care about the Sun light being actually deep red, that isn't the problem, or at least, we have far worse concerns than that.