After a upgrading SharePoint 2007 to 2010, the UI Version is still set to version 3, which makes it look like SharePoint 2007. In order to update the UI to look and feel like SharePoint 2010 to need to run the following script, which will update all site collections. You should save this as UpdateSPUIVersion.ps1, then run it in PowerShell.

Add-PSSnapin Microsoft.SharePoint.Powershell –ErrorAction SilentlyContinue
$SiteCollection=Get-SPSite("http://<SharePointSiteURL>")
foreach($web in $SiteCollection.AllWebs)
{ 
    $web.UIVersion = 4; 
    $web.UIVersionConfigurationEnabled = $false; 
    $web.update();
}