Hi rebasando
I can access your site now and see that you simply add an element 'Image' into the article. Basically, if you want to set the alignment for image / text, this image / text need to be inside an element so that it can be aligned.
I just created a new test article ID: 874 and here are steps:
1 - Add a 'Box' element to article:
2 - Drap&drop the 'Image' element to inside the 'Box' element.
3 - Click on the box >> Typography >> Text Align and set center alignment
You can edit this test article and see the same.