You cannot change a data source type (e.g. .scv --> sql server) You have to copy-past every calculated column, measure and relationship one by one and then finally delete the Original data source tab...
I propose we support this idea, because it would solve this problem among others: https://support.powerbi.com/forums/282523-bi-in-sql-vnext/suggestions/7054789-add-a-data-model-language-for-ssas-tabular
