# What Are the Precautions for Using ECSs?

- Do not upgrade ECS kernel or OS versions. If you want to upgrade the main OS version, for example, from CentOS 7.2 to Cent OS 7.3, use the provided OS changing function.
- Do not uninstall the performance optimization software pre-installed on your ECSs.
- Do not change NIC MAC addresses. Otherwise, the network connection will fail.

Parent topic: ECS Overview