In Magento 2, If you want to Change the Header & Footer Style through Magento Admin, then following are the steps for changing style:
STEP 1: Your Magento Homescreen will look like below:
After Login go to STORES/Configuration as shown in below image:
Go to Magento Admin Panel. In Panel Go to CONTENT>Configuration (In Design).
After that In Design Configuration page, Click on Edit button to edit the theme.
STEP 2: Move the unzip folder.
After that, you will redirect to the Default Store View page.
In Other Settings option, you will see different options like HTML Head, Headr, Footer, … etc.
Now in HTML Head option, you can set your website favicon icon, page title, ..etc.
In Scripts & Style Sheets box, you can add your personal css styles that you want to apply in your header section.
After that, there is a Header Section. In this you can find options to change your logo image, width, height, alt tag and welcome message display boxes to be set.
Below Header Section, there is Footer Section. In this section you can add your personal HTML & CSS codes to apply styles to your footer section of Magento website. You can also change your website Copyright Statement in footer section.
You can also set your Email template logo in Transaction Emails section as shown in the image.
After set all the changes press the Save Config button to save your changes.
STEP 3: After Save Config changes. You will see the message to clean the cache files as shown in the image.
You can directly click on Cache Management option on the screen or go to System->Cache Management (in Tools) to clean the cache files to see your saved changes on website.
Click on Flush Magento Cache button to clean cache of the website.
After Cache clean, go to your magento website & reload the page to see the changes in page.