Good afternoon Laurie!
Generally, in order to do this, you would want to full edit the original purchase transaction. Go to Transactions > Edit or Reverse Transaction. Find the purchase in your transaction list, click on it, and click Full Edit.
Once in the full edit screen, you can change your C+ line to reflect class 8, rather than class 10. Once everything is set back up and balanced, you can record the change.
Let me know if you need anything else!
