You can't delete a round if you've taken payments against an invoice as it's created a fixed point of reference ie income
You can delete customers if they've not been saved as done and paid
The only other way is to go into history find payments and invoices delete them all then delete customers
REMEMBER this will affect your financial history
If a round has no clients or history you can go to system then to round description amend and change names or I imagine delete a round
Hope that helps