To change the theme i found this solution
Go to your Magento 2 admin.
Go to STORES > Configuration > Design > Header.
Click Choose file and select your logo.
Click Save Config.
But Design tab Header is not showing to me
Can somebody help me.
Magento 2.1.2 version.
Best Answer
Please go to Content>Design>Configuration and Edit your store and go to Header Menu.
Thanks I hope it helped you.