How do I make a few simple changes in unit stats?

[Epaminondas]

Hi, I just had a quick question:

How do I make a few simple changes in unit stats for various national units? For instance, I feel the EA Arco pegasus riders are over-costed. I may also bump up the HPs for all commanders.

I emphasize I am not trying to write a whole new mod nation; just a few changes in existing nations. Please be thorough (e.g. do I need to download a utility, and do I have to change re-do the process every time with a new patch?), as I am unfamiliar with modding this game, and just looking at a few stickied threads was an intimidating experience.