Post installation

This was poor planning on my part, but I need to ask for help in fixing it.

After creating a field, and naming it, I realized that I need to use a different field type. But the field name (machine name) is now unavailable.

For example, I first created a field called subtotal. Then I backtracked and deleted that field from my content type, and created a new field to do the same thing. But now I have to call it sub-total. 

https://testing.knut-krueger.de/en/

Two questions:
1. Where did I enter that there are "Vorname" and "Nachname" fields? I can no longer find it and I can't find any untranslated strings

They are used here in the following database fields:

Groups
 simplenews_subscriber
 simplenews_subscriber
 simplenews_subscriber__field_last_name
 simplenews_subscriber__field_first_name
 simplenews_subscriber__subscriptions

I cannot, despite a lot of effort, find any settings for the comment user name. I have looked through all possible pages in comment types, even in content types, even in configuration. I am baffled.

Hi !!
I get this error : The website encountered an unexpected error. Try again later.
 when trying to edit a "image style".
I here is informations I did'nt have any idear about !

<em><blockquote>The website encountered an unexpected error. Try again later.

DivisionByZeroError: Division by zero in template_preprocess_image_style_preview() (line 77 of core/modules/image/image.admin.inc).

Bonjour à tous !

So I have installed the new Desktop App. What a breeze ! I will never go back to MAMP. I have installed Drupal on my Mac to create a photographic library ( Drupal, the new FileMaker Pro ?! ).

But I am somewhat concern : is this a valid long term solution ? I know how to update manually Drupal but what about the Desktop app? Do I have to update the app ? If so, will it recognize my existing Drupal installation ?

I created a Paragraph entity call Address (with fields like address type, street, city, state, country). I would like to link this Paragraph entity to users. So within Drupal's GUI, I went to Manage -> Configuration -> People -> Account Settings -> Manage Fields and added a field for the Paragraph Address entity.  Each user can have multiple Address entities.