This feature is available in Enterprise and Ultimate editions.
You can change the location of Custom Fields on the backlog form by going to the Custom Fields section in Administration, and drag/drop the custom fields in the order that you want them to appear. Please note that you cannot move them above any system fields or mix them into system fields. This will only reorder them in the custom field "section" of the details page.
- From the sidebar, click the admin icon , scroll down to the Asset Customization section and click Custom Fields.
- Move the fields around to get them in the order you want and click Publish Changes.
It might take some experimentation to get them in the order you want.