How to return to display visual upgrade options back after you commit to the new SP2010 visual style
from the site settings / title, description and icon
if you choose “use the new SharePoint user interface, and don't ask me again”
but you changed your mind and said “oh no no i want to go back to v3 visual style", what do i do now ? “
solution:
open power shell
$myweb = $GetSPWeb https://localhost/sites/department1
$myweb.uiversionconfigurationenabled = $true
$myweb.update()
goto site settings now and you will find the visual upgrade option shown