How do I fix an uneven cement floor prior to hard wood flooring install?
A picture might be helpful but I think you have two options:

1) Grind down the ridge.  This will be messy and create lots of dust

2) Use a self-leveling concrete mix.  This is a special mix that starts off almost like water, levels itself and sets relatively quickly. Follow the directions carefuly as usually you have to work with it pretty fast from the time you mix to the time you pour.  It will flow into any cracks and holes so make sure that any of these that might cause problems with another floor below you are sealed before you start.