After upgrade, I got the following message
The upgrade files were copied into the target directory with the '.new' extension. Merge your custom changes into these files and remove the '.new' extensions afterwards.
D:\Websites\TAC8\CMS\App_Code\Application\CMSHttpApplication.cs
D:\Websites\TAC8\CMS\CMSWebParts\Membership\FacebookConnect\FacebookUsersRequiredData.ascx
D:\Websites\TAC8\CMS\App_Code\Global.asax.cs
D:\Websites\TAC8\CMS\CMSFormControls\LiveSelectors\InsertImageOrMedia\Tabs_Web.aspx.cs
D:\Websites\TAC8\CMS\CMSModules\SystemDevelopment\Development\Resources\UICulture_StringsDefault_List.aspx
D:\Websites\TAC8\CMS\CMSModules\SystemDevelopment\Development\Resources\UICulture_StringsDefault_List.aspx.cs
D:\Websites\TAC8\CMS\CMSPages\PortalTemplate.aspx.cs
D:\Websites\TAC8\CMS\CMSWebParts\Membership\FacebookConnect\FacebookConnectLogon.ascx
D:\Websites\TAC8\CMS\CMSWebParts\Membership\LinkedIn\LinkedInLogon.ascx
D:\Websites\TAC8\CMS\CMSWebParts\Membership\LinkedIn\LinkedInUsersRequiredData.ascx
D:\Websites\TAC8\CMS\CMSWebParts\Membership\Logon\LogonForm.ascx.cs
D:\Websites\TAC8\CMS\CMSWebParts\Membership\OpenID\OpenIDUserRequiredData.ascx
D:\Websites\TAC8\CMS\CMSWebParts\Newsletters\NewsletterSubscriptionWebPart.ascx
D:\Websites\TAC8\CMS\CMSWebParts\SmartSearch\SearchBox.ascx
So I made the necessary changes and API changes also.