For any operation purpose, you can change the MTU on the management interface using below steps.
Resolution
1. From Web UI, you can change the MTU of the management interface Device > Management > Management Interface Settings > Edit > MTU
2. From the CLI, the MTU can be configured with the following command in configuration mode:
#configure
#set deviceconfig system mtu <576-1500>
Note: For PAN-OS below 5.0, it is not possible to configure the MTU on the management interface. However, it is possible to configure a management profile and apply it to a dataplane interface in order to manage the firewall via another port. Dataplane ports can be configured for a specific MTU.