Marketo email editor has fewer features than tools that focus exclusively on email sending. So, you are not able to edit the design as easily as you might hope by removing one of two columns (and having it transform into a single column module, for example). When advising on new templates for clients, we recommend thinking in terms of the combinations you would like....have a separate "button" module so you can easily have a content module with or without the button, for example.
If you are comfortable in HTML and the option is not locked in your instance, you can also edit the code by clicking on the "Edit Code" button at the top of your email.
Or suggest additional modules that should be created in your next template review. You can see all the Marketo options here: https://experienceleague.adobe.com/docs/marketo/using/product-docs/email-marketing/general/email-editor-2/email-template-picker-overview.html?lang=en
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