Azure Front Door supports upgrading from Standard to Premium tier without downtime. Azure Front Door Premium supports advanced security capabilities and has increased quota limit, such as managed Web Application Firewall rules and private connectivity to your origin using Private Link.
To learn more about the difference between Standard and Premium tiers, please see Azure Front Door tier comparison | Microsoft Learn.
To learn more about how to upgrade from Standard to Premium tier without downtime, please refer to Azure Front Door Tier Upgrade.