If you need to change which spouse's record is set up as the Family Head for a particular family, you can accomplish this in the following manner:
Go to one of the family member's records and click their Family Name in the Basic Information section:
Then, on the Family page, click the Actions menu and select Change Head:
You'll then see a modal where you can select a different family member to set as the family head:
Here, select the new head and then click "Reset Family Head".
Note: after changing a Family Head, your previous Family Head will now have a Dependent relationship of "Other". You can edit their relationship to the Family Head to reflect the proper relationship, something you may need to do with the other dependents as well, if their relationship to the new Family Head is different than it was to the previous one.