change item from old to new

I have one item his inventory is not 0 meaning inventory of item card is big from 0 his unit of measure is by ton and i need it by kg so that i decid to solve the proplem to create another item with same name then transfer his transaction to new item then block old item

How i make transfer this item from old to new ?and if i make this are this will conflict with old item please reply for me

thanks