As of version 3.1 the extra fields are ordered differently than previous versions. However we will leave the original documentation below.

In v3.1 a new column is added on the far left labeled "Order". To change the order of an extra field you will use the drop down and select the number where you want the extra field to be moved to.

In v3.0 once you've created more that one extra field, another column will appear in your extra field list named "Order".

If you would like to change the order in which your extra fields are displayed, click the up arrow to move the extra field one position up