To change the header margins in Microsoft Word, you can follow these steps:

1. Open Your Document: First, open the Word document for which you want to adjust the header margins.
2. Go to the Layout Tab: Click on the „Layout” tab in the Word ribbon. This tab contains options related to page layout and formatting.
3. Click on Margins: In the „Page Setup” group within the Layout tab, you will see an option labeled „Margins.” Click on the drop-down arrow next to „Margins” to reveal a list of predefined margin settings.
4. Select Custom Margins: Scroll down to the bottom of the predefined margins list, and you will see an option called „Custom Margins.” Click on it to open the Page Setup dialog box.
5. Adjust Header Margins: In the Page Setup dialog box, you’ll find a section labeled „Margins.” Here, you can adjust the margins for the header of your document. Look for the „Header” field, and input the margin value you want. The header margin is typically set in inches or centimeters.
6. Apply Changes: After entering your desired header margin values, click the „OK” button to apply the changes.

Your header margins will now be adjusted according to the values you specified. Keep in mind that changing the header margins will affect the space between the top of the page and the header section of your document.