How to edit the Units and buildings skin design or paint design? please elaborate decently to me thanks would appreciate it

This should be in the generals modding thread.

Anyway, what you want is to change (or replace) the texture of the models.
I don't know the exact steps (as I am a coder and I don't deal with models) but I can give you a rough guide and a modeller should be able to fill in the gaps (and correct what I get wrong).

First you need to edit the texture (or create a new one) and save it as a .tga file.
(I'm not sure about this next step, you might need it, you might not.)
Then define the texture in an artwork ini file (I'll get back to you on this)
Then open the modelling program (I think it's called gmax and you need a plugin called renx) and replace the texture there. (I can't give any more information about the program as I don't use it).

As I said I don't deal with models but I will come back to you and fix up some of this information once I've checked it out.

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What game are we talking about here?

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Where is the modding thread for Generals

Start Here 

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Make sure youd already seen the Tutorial in Generals Modding Section and Seen the Tutorials of Mr AcidBrain in the Forums

Edit:
I Already Know How to Do A New Model and Skin it But Due to ... Some Issues And Needs In Adding a Unit is stop for now.

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This could, possibly, be helpful as well:

http://killasmods.gamemod.net/page.php?file=tnkskn2 

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