Change Page Layout via SharePoint 2010's Publishing Site
For good practice, choose your page layout type on your SharePoint 2010 publishing site before entering any page content; although you can change page layout types later, that sometimes leads to unexpected consequences.
To create a new page, choose Site Actions→New Page, give your new page a title, and click the Create button. Your new page appears, with the site’s default page layout applied. In publishing sites this should be a Body Only Article page.
Follow these steps to choose and apply a new page layout to your new page:
Make sure you're in Edit mode, for example by looking for the Editing Tools tab.
If you aren't in Edit mode, click the Edit icon above the Ribbon (it looks like a piece of paper and pencil).
You can also click the Page tab and then click the Edit icon. The Editing Tools tab appears with the Format Text and Insert tabs in it.
Locate the Page Actions section on the Ribbon.
The Page Actions section is on the Page tab. This section includes the Preview, Page Layout, Make Home Page, Incoming Links, and Draft Check options.
Click the Page Layout drop-down list and choose a page layout.
The page layouts available for this site are shown, grouped by type, with a thumbnail representation of each layout.
Think about the contents of your page to make sure the layout is what you need.
Edit the content as you normally would, and be sure to select Save and Close or Check In on the Page tab when you’re done.
Your changes are saved and the page is no longer in Edit mode.
The steps to change the page layout after you enter page content are no different than those to choose the initial page layout. But you should choose the new page layout carefully; does it have the same containers as your current page? Will you need to rearrange a lot of the content?
If your current page uses Web Parts and the new page layout doesn't have a corresponding Web Part zone, the Web Parts will either move to another zone or close. Content in controls (such as byline and date) will disappear if you apply a layout that doesn't contain those fields.
However, simple changes, such as going from an Article Left page to an Article Right page (where the only difference is the location of the image), go very smoothly.