Go to Geffen
Talk to Barend Ugarte (Equipment Socketing NPC).
The NPC will ask you to bring 11 items. 1 item will be converted to  slot or 1 slot will be added to a weapon limiting to a 2 slot item.
1x Light Saints Armor  (will become slotted).
10x Light Saints Armor  (will be consumed by the NPC).
100,000 – 150,000 zeny (Depends on the items but mostly that is the range).
Product = 1x Light Saints Armor 
if Weapon then it will become Bow