I have multiple items in different sizes and I use the stock attributes. Let's say I have 2 size medium in blue and 1 size small in red. When the customer orders and chooses the 1 size small in red, the qty should automatically change to zero and not allow another customer to order that same option. However, unless I remove the attribute manually, the customer can still order it . How can I correct this without having to change things manually all the time?