Hi thiagonmat,
You can open the article and select layout-1 in the Options tabs
Or Configure the article layout for your site.
Go to System > Global Configuration then select Articles. In the Articles setting, select the layout and save.
If you want to change the image size for the Default layout, you can add the following CSS code:
@media (min-width: 1400px) {
.item-page.layout-default.no-sidebar .full-image {
margin-left: auto;
margin-right: auto;
max-width: 1600px;
}
}