Hello @Pinonono,
Hope you are doing well and thanks for asking the question.
Can you clarify whether you want to remove the thumbnail pic when viewing listing of all blog posts or only when you are viewing a single post?

Regards!!

@Pinonono – If you need to remove thumbnail picture from all blog posts make the following settings:
Go to Appearance-> Customize-> Theme Options -> Layout Options->Archive Layout ->
Select Post Excerpt from dropdown.

And, if you need to remove thumbnail from all single individual post/page make the following settings:
Go to Appearance-> Customize-> Theme Options -> Layout Options->Image in Single Post/Page ->
Select No Image from dropdown.

When you are done with the settings click SAVE & Publish.

Let us know how it goes.
Regards.