Hi Javier,
Thanks for reaching out with your BoldGrid Post and Page Builder questions!
In order to adjust your column sizes you’ll need to use the Advanced Controls provided by Post and Page Builder. If you hover over any one of your columns a “blue” hamburger tab will appear. Click the hamburger then scroll down and select “Advanced Controls” and from this section you’ll have the ability to resize the column or change it’s shape.
If you want to have absolute control over the column and you’re comfortable using custom CSS then you can add a custom class or ID to each column and select it in the CSS/JS editor section of the WordPress Customizer to make your changes.
I hope this helps! Please let us know if you have any other questions for us.