help with trigger for items

[Chailman]

hi , i want to do a trigger that change an item for another , when arthas pick or buy ``big orb`` the item that appers in his inventory is another like `` arthas big orb`` because i make a lot of heros and a lot of especial abilitys that active with the item , so i make a lot of similars items but only one is in the store and when it sells change for another item depent of the hero.
and i m very bad in condiccions , would you please show me how to make the trigger ?

forgive my english , i dont practice in a long time

 

[Dr Super Good]

When a hero purchases the item, remove it and give the hero the replacement item.

Make sure the item is the orb type and the buying unit is of type Arthras.

 

[defskull]

A test map attached.
The orb changes to its corresponding holder
If the "Base Orb" has been modified into another orb, it cannot be modified any longer