Edit the Product Set at Blending / Setup / Product Sets, and, in the Product grid, uncheck the Active checkbox for the old Product.
When formulating Blend Tickets, inactive Products are not considered in the formulation. If this Product may be used again in the future, it may remain in the Product Set as inactive. If this Product will not be used again, it may be deleted from the Product Set by selecting the line number in the Product grid to highlight the row and then using the Delete key on the keyboard.
A new Product may be added by double-clicking on the next available line in the Product grid and selecting the Product. Mark the Product as Active and save the Product Set.