1. Start in your vcita account. 
2. Go to Settings > Staff (just Settings for non-admins).
3. Click the ⋮ icon next to the staff member you want to sync the calendar to and click Edit Staff Settings. 
4. Switch to the My Schedule tab.
5. Click Edit sync preferences next to your synced calendar.

6. This will take you to your Calendar sync Wizard where you can Disconnect from your currently connected calendar:
7. When clicking on Disconnect, you'll get the option to keep exported vcita events in your external calendar or to have them automatically removed from it.
8. Once you've disconnected your external calendar, the same wizard lets you reconnect to any other external calendar:

Further Reading:

• Sync Your Google Calendar to vcita
• Sync Your Outlook Calendar to vcita