# How to upgrade the Bun version


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

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