How do I remove restrictions on my iPhone?

Restrictions added to Apple devices by Mobile Device Management or Parental Controls are made at a very low level.

No amount of "thumping on it" by changing settings and using ordinary process is likely to remove them.

Using extraordinary means such as attempting to delete MacOS, IS likely to make your device so that MacOS can not be re-installed, and is therefore completely unusable.

If you are a minor then you need to get permission from your parents/guardians.

Read here=> Set up parental controls with Family Sharing on iPhone – Apple Support (AU)