Header image size

Greetings! I have the Adventurous Pro theme. The header images is limited to 1600 × 400 pixels. How can I update a larger image? My site. https://fieldnotes.media/ I would like to have a large header with the same theme. More like 3000 × 1408 Example: https://jonnajinton.se/ Please let met me know how to update. Thanks, Jannet Walsh