i have a mace that i love and at the moment i can improve it to exquisite..but as this is a deadra mace i dont want to do it unless i can upgrade it to epic/legendary later..so my question can an item be upgraded twice?

At least for some, yes. My plate armor is Flawless for example. So I think there's 3 levels of improvement.

I think flawless is max level. It's the best the low level stuff gets at 50 smith when high level is still only exquisite.

you can upgrade an item as many times as you want if its possible to get it higher that it already is.

Upgrade a steal sword at smith lvl 20, then again at lvl 40, again at lvl 100, then again when you perked the steal smithing. Still not enought, drink a smithing potion and have some gear with smithing enchants to get it even higher.
If the item is enchanted already you need to get the enchanted perk from the smithing tree.