Select the "Upload" tab and browse for your downloaded file.

If you want to "download" a header rather than making one from scratch, these platforms offer pre-made templates:

A custom header does more than just look good; it improves your data collection:

To get the perfect look for your survey or quiz, you don’t actually download a header from Google Forms—you upload a custom image to it. Google provides a library of stock headers, but using a unique design makes your form look professional and trustworthy.

Adds a logo so respondents know the form is official.

This is the "Customize Theme" button in the top right corner.

A great source for aesthetic and seasonal header inspiration. How to Upload Your Header