Wow, this seems like an interesting and much requested feature I just discovered in SharePoint 2010. It seems you can now change the page layout of an existing page! Maybe this is old news already, but I hadn’t heard anything about it yet.
So we have our regular article page right here:
SP2010 Article Page
When you expand the Page Layout button on the ribbon, you get this:
SP2010 Change Page Layout
Let’s for example select Blank Web Part page as the new layout for our page. SharePoint then takes the new setting, doesn’t perform a post-back anymore, AJAX is very nicely integrated now:
SP2010 - Changing Page Layout
When SharePoint is done processing the changes, our page is now a web part page instead of the article page it was before!
- SP2010 – Web Part Page
Edit:
The functionality isn’t completely bug-free yet. After playing around with a couple of different page layouts, I’m suddenly getting this error:
- SP2010 Change Page Layout Error
Obviously the product is still in beta, I’m sure this will be fixed in the final version 
no its not fix :p
Right this is the issue with SharePoint and not really with your own layout. Clearly you have 2 definition for same element thats what the error suggests.
Read the error they are informative if you read them.
I don’t know, I was just playing around with the out of the box stuff at the time. The error to me seems to indicate that SharePoint somehow changed the page contents and added another sitemap control or something. I never really looked further into the issue though.
This is also possible in MOSS 2007
Maybe I’m just blind, but where are you seeing Page Layout on the ribbon?
I don’t see it showing up on the ribbon provided by Edit Page, and the one in your screenshot appears to show the Settings group for a Library ribbon. I’m lost.