Upgrading/Migrating a SS3 Database to SS4

Silverstripe Version: 4.13

Question: How can I migrate/upgrade my old ss3 database to ss4?

I tried to upgrade a SS3 Project to a SS4 project and did all the filesystem changes, namespacing, environment managing and stuff. If I run the project with the default SS4 database it works fine and I dont get an error. But if I paste in my old SS3 database, run dev/build and also the MigrateFileTask I dont get an error also but the resources and .ss files dont seem to be applied.

Thanks in advance