How to decrease the polygon count on my mesh? I'm an absolute beginner. I'm trying to reduce the count of polygons in my mesh.

I've looked at some tutorials online and I know what I need to do is go through the decimate process.

I can't locate the decimate function on my interface.
Can someone please show me how to find the "decimate" menu in my interface. The interface is unedited from the stock install.
The simple answer is Mesh > Clean up > Decimate Geometry.

Then look in the bottom of the Tools panel to see the Decimate options and reduce the Ratio.



A better, non destructive option is to use the Decimate Modifier

You will find more options there. 



There seems to be an option which tries to keep UV maps intact which would be important if your mesh is using those.