this place can be useful for helping with both terminology and mechanical procedures, so long as you're open to correction and being asked for clarification

You'll need the correct freewheel-removal tool to get the freewheel off, and then you can replace the axle.

Sheldon Brown's website has lots of useful information, including a page explaining the difference between freewheel and freehub/cassette designs.
Here's a picture showing the difference: