To accomplish this, you will want to follow these steps:
Navigate to Administrator → Extensions → Templates Manager and select the template you are currently using as your default.
Navigate to the Layout tab.
Add the number for the Page Width you want to have for your site in px.
In Page Align select Left , Right, or Center depending where you want to position your site.
- For SECTION MAIN CONTENT select the style for 2 columns and 3 columns.
Also select for each part of the template the style for 2 columns, 3 and 4 columns.
- Click Save button
Your site will get the layout you select.