Night Elf Female > Undead Male

[Éin]

Hi,

I'm very new to this model-changing business. I'm awfully tired of my female night elf model and I would absolutely love to change it into the undead male model. Could someone "do this for me" (although, I admit, I have absolutely no idea how this even works) or direct me so I can do it myself? Also, is it possible to change particular weapon models?

Lastly, this is still legal, correct?

Sorry for spamming questions. -.-

Thanks,
Éin.

EDIT: I'm on a Mac - I don't know if that matters at all, though.