Recent attempts to take shots with my Canon Powershot A470 have resulted in way over-exposed images. How do I correct this?
It depends the amount of over-exposure. Any area which has been blown out cannot be recovered but the image can be darkened to look more natural if most of it is not clipped.
Lightroom is the tool of choice for this and there is a free trial available should you want to see it for yourself. You can interact with a histogram directly or move the highlight slider towards the left for example which would recover from the brightest part of the image as much as is possible.
go to the menu and search for the +/- sign, that says something like exposure correction or exposure ajustment. and then turn it down. normally a value of 0 should give normal results. maybe someone accidentely pushed the value up a litte.