upping a weapon

[Creatures]

i have a eth naga and i am trying to up it but im not sure of the formula?
does it require non sockets or sockets?

[Evrae Altana]

You can't upgrade that. You can only upgrade rare and unique items.

[Creatures]

wuts the different between rare and unique?

[Evrae Altana]

Rare item names appear in yellow, and can have anywhere between 2 and 6 randomly generated mods. Unique item names appear in gold, and have unique names and attributes.