Learn how to remove an administrator without deleting the user from the group on WhatsApp in the following tutorial. To use the function on Android, I need to have the test version updated (from 2.18.41) and have Android 5.0 (Lollipop) or later.
Step 1. Open the menu of a WhatsApp group and select the option Group data.
Step 2. Tap on a group administrator that you want to remove and hold to open options. Select Remove as admin. Then, you will see that the user remains in the group, but without the administrator status.
Basically, the messenger changed the way to remove administrator privileges. The rest of the functionality remains intact.