Done!! I followed the steps you told me:
1. I modified the Course folder aggregation method to "Weighted mean of grades", and max grade: 10.00
2. Then I created one subcategory:
- Category name: Topic Quizes
- Aggregation: Mean of grades
- Maximum grade: 10
I moved the 14 quizes inside that folder and set the weight to 4.0
3. I weighted the global quiz to 6.0.
That's it!! It was easier than I thought!
Thank you for your help!