Starting version 3.x ?? the Management Center is allowing the upgrade to new versions via the GUI.
For previous version please use the below Tech Doc article to upgrade.
https://techdocs.broadcom.com/us/en/symantec-security-software/web-and-network-security/management-center/3-3/admin_mc/upgrade.html
Before starting the upgrade refer to the below KB and create a backup of Management Center and read through Potential issues and Upgrade Best Practices
https://techdocs.broadcom.com/us/en/symantec-security-software/web-and-network-security/management-center/3-3/admin_mc/upgrade.html
1. In the Management Center GUI go to Administration > Image Management
2. Click on the Add Image button
3. Either upload the image locally using Drag and drop or Select a file to browse your computer. Another method is to point to a http/https server containing the .bcsi file you want to upgrade the appliance with. Confirm by clicking the Upload button.
4. After successfully uploading the image it will be shown on the list in Administration > Image Management . Confirm the new image is marked as Default.
5. To start the upgrade process you will need to click the Reboot Default image button