How to Add +13 to +15 in Version 5165

hello guys, i want to add +13 to +15 items

i have the npc who compose it, but +13 to +15 hasn't effect(no bonnus)

how can i add the bonus to (+13 > +15 itemps ) please

thanks

Do a check for the item.
Item I = new Item();
if (I.Plus = 12)
{
I.Plus =13;
GC.MyChar.CPs -= 100;
}
Also do a check to see if the character has the required amount of cps.