You can upgrade Gold Equipment to higher level equipment by going to the Doran (Equipment Upgrading Master) in the City of Heroes.
Equipment upgrading will consume blood soul hearts and gold materials every time you upgrade your equipment.
After you have upgraded your equipment to level 70, the next upgrade level will require an Elf Stone to upgrade your equipment from level 70 Gold Equipment to level 70 Orange Equipment.
Orange Equipment is extremely rare and will give your character more additional attributes once the equipment has been identified.
Please note: Elf Stone can be found by completing instances or purchasing it from the prepaid market.