Is there a way to edit or delete palettes? CS 40AV?

Just re-record over the top!

Remember that palettes are what we call "referenced data".
This means changing a palette will automatically update every cue and memory that uses the palette.

This lets you quickly correct a position, color or beam thoughout the entire show.
As you're taking something over you will need to be careful about which palettes you're repurposing.

I'm aware of the consequences and they're something I can live with. My question is, can it even be done, and how?

For example, I have palettes named 'Wide' Very Wide' 'Med Wide' - essentially useless when I want to know percentages. Or 'Stage L'; well, that's a large area, Stage L doesn't do much good. 

To edit or update a palette, simply record your new values over the top.

To edit or update a palette, simply record your new values over the top.