Mammon upgrade of dual C-grade

If I create a Dual C-grade, then enchant them to +4 will I then loose the enchantment if I upgrade them to better Dual C-grade by using AA at mammon?

Yep all added stats will be lost.
If u exchange it to a semiliar weapon, for instand fists, the stats on it will be same.

For instance mid C-grade duals > Top c-grade duals (enhanc. are lost)
mid c-grade duals > mid c Fists (enhanc. will be saved).

as a side note, you can't exchange duals for any other weapon. they can be upgraded (and they lose any enchantments) or exchanged for similar duals with the same pattk (and they don't lose their enchantments), but you can't trade, for instance, duals for fist weapons, or vice versa.