how to transfer all events from one calendar to another

1. Create a new empty iCloud calendar from Calendar ➔ New Calendar ➔ iCloud
2. To copy a calendar, click on it from the menu that appears when you select the calendar button (top left corner of Calendar) to highlight it and choose Calendar ➔ File ➔ Export ➔ Export (export it to your desktop for ease)
3. Double click the exported file and choose the new empty iCloud calendar to import them into.
4. Ctrl-click on the original calendar from the menu that appears when you select the calendar button and choose delete.
5. Repeat for each calendar.

Unless you have access to a computer, you can only do this event by event.

Yes, those are instructions for a Mac, I would have thought that windows would have some similar kind of proceedure for moving or merging calendars and events.

I'm sure there are others such as Outlook etc.