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+The following steps can be followed to update a Webpacker v3.5 app to v4.
+
+1. Update the gem `webpacker` and the package `@rails/webpacker`
+1. Merge changes from the new default [.babelrc](../lib/install/config/.babelrc) to your `/.babelrc`. If you are using React, you need to add `"@babel/preset-react"`, to the list of `presets`.
+1. Copy the file [.browserslistrc](../lib/install/config/.browserslistrc) to `/`.
+1. Merge any differences between [config/webpacker.yml](../lib/install/config/webpacker.yml) and your `/config/webpacker.yml`.
+1. Merge changes from the new default [postcssrc.ym](../lib/install/config/postcssrc.yml). Specifically, rename `postcss-cssnext` to ` postcss-preset-env`.
+
+Here is an [example commit of these changes](https://github.com/shakacode/react_on_rails-tutorial-v11/pull/1/files).