I have not been able to delete inventory items that are no longer required.
I have clicked on “edit” the item and then clicked on delete but it will not “delete”
Yeah, that is a “feature”. Once inventory item has been used in some transaction, it cannot be deleted. If system would let you delete it, it would break integrity of historical data.
There is going to be Archive function which will allow you to archive customers, suppliers, inventory items, accounts etc, which are no longer used so they are not shown prominently in various lists but still kept in the system for the purpose of historical records.