New user, new unit!

Number_21 writes: Hi everybody!

I've just downloaded Advanced Genie Editor 3.

I would like to balance the civs a little bit.

I'd like start changing the Persian unit "Militia" in another unit with different name, hp, resourses.
I'd like to maintain all others characteristics (where is built, graphics, etc.)

Could you please give me a step by step tutorial?
(or a link to it :-) )

edit: where I have to save the modded file?


Thank you very much!