This tutorial will show you how to change the logo image in transactional e-mails of your Magento 2 store. Please follow below steps to add new logo for emails in your Magento 2 store.
1) Log in to Magento 2 using your admin account.
2) From left sidebar, click Stores, and then Settings -> Configuration.
3) In this page, expand GENERAL section in the panel on the left and choose Design.
4) Now select Emails tab.
5) Browse your new logo at Logo Image field.
6) Set extra options like Logo Image Alt, Logo Width, Logo Height, etc.
5) Click on “Save Config”.
6) Clear the cache.
Thats it. Now you can check new uploaded logo in your store emails.