Keep in mind this is an advance modification to your site and we recommend checking out our Custom Code article before proceeding.
Entire website
To remove the header/footer from your whole website inject the code through the CODE option under Settings. (This section is used for code affecting your whole site)
Place the following code in their corresponding locations:
Header
<style> #sp-header { display:none !important; } </style>Footer
<style> #sp-footer { display:none !important; } </style>
Specific Page
To remove the header from a specific page, go to the page editor and select page settings, then the Code tab. Inject this code to the header and/or footer code sections depending on which code you are trying to use.
Once you have injected the code to the desired section, just save your changes (for pages edit make sure to save and publish) and you are good to go.
Don't forget to Publish!