To remove payment plan from an existing order:
  1. Click People tab 
  2. Use search field to find customer 
  3. Click name of customer 
  4. Under Order history tab, click desired Order number 
  5. Underneath Make a Payment button, click Remove Payment Plan 
  6. Follow prompts
  7. Click Submit
For additional information about adding a payment plan, use the following article: Add Payment Plan to an Existing Order

Note: Once payment plan is removed, all remaining balances appears on order and customer will need to pay balances all at once