DELETE SUBNET:
You can delete a subnet only if there are no resources in the subnet. If resources are in the subnet, you must delete those resources before you can delete the subnet.
CHANGE SUBNET:
If no resources are deployed within the subnet, you can change the address range. If any resources exist in the subnet, you must either move the resources to another subnet, or delete them from the subnet first.
原文：https://www.cnblogs.com/chun2021/p/14778970.html