Hello,
What is the recommended way to update a board by deleting all the existing items and then replacing them by new ones? Do I need to delete every single one of them one-by-one and then adding them one-by-one ?
Thank you
Aloha @CacttusMan 
As you’re looking to remove all of the items on a board, as opposed to removing them individually one-by-one, I believe the below workflow would be significantly easier and result in you needing to ping the API less:
- Add a new group to the board
- Delete the previous groups on the board - this will delete all of the items within those groups as well
The reason I suggest first adding a new group is because monday.com’s structure requires that, at all time, at least one group needs to be on the board. Even if that group has no items within it, there must still be a group on the board 
-Scott