How easy is it to change a water pump of a 2004 chevy impala?

not to hardHow easy is it to change a water pump of a 2004 chevy impala?if it is a 3.1 or 3.4 liter engine it's fairly simple to acsses and change but if it is a 3.8 liter it will be harder to change but regardless of which engine you have getting the air out of the cooling system after the install is tricky and you don't want an air lock.