In order to upgrade your 3.x site to 3.7 SP4 .NET 3.5 / .NET 4.0 so it can be migrated to 5.x, you need to download a patch from your 3.x downloads section of the site - the archive is called hotfix for 3.7 SP4 ( please check the attached screenshot ). Basically what you need to do is modify the webconfig file with the one from the archive and merge all the files. The upgrade instructions are as follows:
1. BACK UP the project! It is extremely important that a backup is done of both the files and the database before installing anything new. This ensures that whenever anything goes wrong, no information is lost.
2. UNZIP the patch archive in a temporary folder! Then copy all the unzipped folders and files in the project folder. If you unzip directly in the project folder, you will have to replace all permissions as the new files do not inherit the project's permissions.
3. IMPORTANT. You need to check that changes you made to some of the project files are not replaced during the upgrade. Please note that we are no longer overriding your control templates. By default, Sitefinity will use its own embedded templates both for the back-end and the front-end. In order to use your customized control templates, you should map a view to each of them. This is described in the KB Article How to map a view to an external template, in Sitefinity?
4. There are no changes in the web.config file for Sitefinity 3.7 SP4 .NET 2.0 and .NET 3.5 builds since version 3.7 SP3. If you are upgrading to Sitefinity 3.7 SP4 .NET 4.0 build you must compare your original project web.config file to the new_web.config file from the upgrade archive. Change your original web.config to reflect the changes introduced in this version. You can use any comparison tool you like.
5. Merge the existing file ~/Sitefinity/Admin/ControlTemplates/Pages/PageHistory.ascx. If you do not have any custom code in that file, you can safely replace it with the one in the archive.
6. If you have changes in the WikiviewSingleItem control template - you should download the external templates archive for the latest version of Sitefinity 3.x and merge your changes with the template.
You need to start the Search Indexes. Otherwise, you will get error messages if you try to publish content. To start the Search Indexes, go to the administration area, Administration tab, section Services -> Search and start all indexes by clicking on the Start indexing links.
7. Open the folder ~/Sitefinity/ServiceAssemblies and make sure you delete the assembly there. When you initialize the Newsletters module, it will be recreated. If you don't do this before you apply the patch, you'll get the following error:
"Unable to load one or more of the requested types. Retrieve the LoaderExceptionsProperty for more information."
8. If you have several Sitefinity projects connected to one database, please make sure you upgrade all of the projects to the same version.
9. If you are moving your files from Sitefinity 3.7 to Sitefinity 3.7 SP4, please make sure that you move App_Data\Wikis.xml file as well. This file is the storage file for the Wiki module.
10. If you have custom modules and controls, that have references to Sitefinity assemblies, you should rebuild them referencing the new assemblies. In case that you are upgrading to Sitefinity 3.7 SP4 .NET 4.0 your projects should be rebuilt targeting the .NET 4.0 framework.