See "How do I edit my research item's details?" in https://explore.researchgate.net/display/support/Reviewing%2C+featuring%2C+and+editing+your+research for instructions. However, it is not possible to change the type from Preprint to Article. You have to create a new page for the published version, but you can link both pages. See my reply to this question for explanations and instructions: https://www.researchgate.net/post/Can_I_merge_a_preprint_and_the_published_version_in_one