2005 Chevy Impala Over Heating

Start by making sure you have enough coolant (with engine off and COLD, your level is at/slightly above the cold mark on the overflow tank, and no lower than the bottom of the radiator neck). If your level is low, add dexcool coolant and inspect the cooling system for leaks.
I would also replace the thermostat as a lot of cooling problems are associated with a bad thermostat. There are more potential culprits, but try that first and come back if it fails to fix your problem.