# How to upgrade the Python version


You can upgrade or downgrade your Python service to a different major Python version by setting the [`run.base`](/python/how-to/build-pipeline#base-1) parameter in your `zerops.yaml`. When you [trigger a new pipeline](/python/how-to/trigger-pipeline), Zerops will start new runtime container(s) with the required Python version. If you don't specify the `run.base` attribute in your `zerops.yaml`, Zerops keeps the current Python version for your runtime.

If you want to build your application with a different major Python version, change the [`build.base`](/python/how-to/build-pipeline#base) parameter in your `zerops.yaml`. The `build.base` is the required attribute.