In order to migrate to 5.x, your Sitefinity version should be 3.7 Service Pack 4. You have to create a new empty 5.x project and setup the 3.7 project for migration. The setup can be done manually or automatically using the Project Manager of Sitefinity 5.x. If Project Manager has access to the web.config file, then automatic setup with project manager is a better solution. In case Project Manager does not have access to the web.config file, you have to setup your 3.7 project manually. Here is a helpful link:
Once you have your 3.7 site set up for migration, you have to copy all resource files and folders from the old 3.7 site to the new 5.x one. App_Master, App_Theme, custom controls, images, scripts and documents need to be copied manually from the 3.7 to 5.x site.
And the last step to migrate is to run the migration process. The migration process is started by the new Sitefinity 5.x. To accomplish this, open your 5.x project. On the dashboard there is a link to the migration module. Click on "Migrate your site from Sitefinity 3.7 SP4 to the newest version". You have to type the URL of the of 3.7 site and admin credentials.
Here is a link with overview and considerations about Migration module.
Hope that this would be helpful.
the Telerik team
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