If you want to change the logo of your Magento store, Please follow the below steps.
Log in backend and open content theme configuration.
Content -> Design -> Configuration
Content -> Design -> Configuration->Select theme configuration
Open Design theme configuration and select theme which enabled in your storefront.
Content -> Design -> Configuration->Edit theme configuration->
Edit your theme which is enabled in your storefront and upload new logo which you want as new.
After did all the above steps you need to clean cache via terminal.
php bin/magento cache:flush
Good Luck, Hope this solution useful for you.