In the past changing a field name required you to run a content migration script to move the content from the old field to the new one. Now you can just rename the field and all your existing content will be migrated to the new field automatically in the background.

Section titled How to prepare your code for the migration How to prepare your code for the migration

If your project is already live you need to include a logic in your code to render both fields during the renaming process. Following an example in Vue.js (assuming you rename family_name to last_name:

<h2 v-if="blok.family_name">{{ blok.family_name }}</h2>
<h2 v-if="blok.last_name">{{ blok.last_name }}</h2>