1. Login in your mailwizz app then go to Backend > Extend > Extensions

2. Open your (s)FTP client and upload the contents of the support-tickets folder in apps/extensions/support-tickets/ folder so that you replace the existing files with the new ones.

3. Go back to your browser and refresh the Extensions page.

4. You will now see the upgrade button for your extension. 
Click it in order to proceed with the upgrade process. 
Please note that not all extensions might have the upgrade button, which is fine. 

If the button from step 4 is missing, it means all you have to do is step 1, 2 and 3 and that step 4 is not needed anymore.