woocommerce shipping fee issues

Hi there!!
I’m using woocommerce for quite some time now. No problem.
I used to do dropshipping but now I’ve purchased some products myself in order to make quicker deliveries. Those deliveries have a cost.

When someone wants to buy one of this products I have no problem. The customer has the option of a free shipping (“slow”) or a “fast” shipping.

My problem arrives when someone wants to buy several products and one of them has the option of this “fast” shipping.

How I can make woocommerce disable this “fast” shipping option when someone wants to buy both kind of products (“slow” and “fast” shipping)?

Thanks!!!

The page I need help with: [log in to see the link]