How do I change a role to parent

From the link I provided earlier (because Apple's copy and paste does not work for me with my browser you might just find it easier to go to the link and near the bottom you can read for yourself):

How to choose another approver

The family organizer can give another parent or

guardian in the group over the age of 18 permission to manage Ask to Buy

requests. Only one adult needs to manage each purchase, and after the

purchase is approved, it’s final. 

On your iPhone, iPad, or iPod touch

In iOS 16 or later:

1. Go to Settings.
2. Tap Family, then tap your family member's name.
3. Tap Parent/Guardian.
4. Tap Set as Parent/Guardian. 

In iOS 15 or earlier:

1. Go to Settings, then tap your name.
2. Tap Family Sharing, then tap your family member's name.
3. Tap Role.
4. 
   
5. Tap Parent/Guardian.
6. 
   

On your Mac

In macOS Ventura or later:

1. Choose Apple menu  > System Settings, then click Family.
2. Click a family member's name.
3. Click Parent/Guardian.
4. Select Set as Parent/Guardian, then click Done.

In macOS Monterey or earlier: 

1. Choose Apple menu  > System Preferences, then click Family Sharing.
2. Click Family Sharing in the sidebar.
3. Click Details next to the family member's name.
4. Click Edit, then select Parent/Guardian.

There is no role of "parent."

There is the role of Organizer. In order to change the Organizer you would have to disband the current Family and start it up again with a new Organizer.

There is also the role of Approver if you turn on Ask To Buy. The Approver is often another parent but can be any adult.