how do i change a water pump ?

If you have to ask,I assume you are not yet a very experienced mechanic.
There is nothing horrendously technical involved but you will need to be accurate and methodical.
Actual method depends on model year/engine code.
You will have to take the timing belt off to get at it, so it's always best to fit a new belt, idler rollers and tensioner.
Basically it will be something like-
drain coolant
jack up front OS, fit axle stand, remove wheel.
remove plastic access panel on lower inner wing
remove airbox
remove spark plugs
remove upper engine damper mount
remove aux. belt
remove cam belt cover
set cyl. 1 timing to TDC using cam/crank pulley marks
fit cam lock
slacken tensioner
remove cam belt
remove idler rollers and tensioner
remove water pump (which will be seized in the block and be an absolute ****** to get out)
then it's just a case of putting it all back together, making sure you line it all up properly, tighten everything to the correct torque values and fill with fresh anti-freeze.
This is not a definitive work instruction, merely a general guide.
If you intend to tackle the job buy the Haynes manual.
Be aware that if you get it wrong you could wreck your cylinder head.

dingus
June 2009