The Sun will turn into a red giant in approximately 4-5 billion years from now when it exhaust all of it's hydrogen, and destroy all the inner planets, including Earth.
But there is bad news before that happens to life on Earth; every second the Sun burns up it's nuclear fuel, turning mass into energy, and it must make up for this loss of mass by increasing it's temperature. The Sun will become so hot in approximately 600 million years that all vegetation will die out. When this happens the food chain will collapse, causing catastrophic results for most life on Earth. The Sun will continue to heat up and in approximately 1.2 billion years from now the oceans will start to boil-off and evaporate. By this time most life will have become extinct (except maybe microbes). It will remain like this until the Sun core uses up all of it's hydrogen and then fuses helium, causes the red giant stage. When this red giant stage finishes it will become a white dwarf, saying to the universe...we were once here.