Click Artwork > Pieces in your left-side menu
Click on the Piece with the Appraisal you want to edit
Go to Appraisal History on the right and click "View" on the Appraisal
Click Edit Appraisal
Click Delete
The records associated with the appraisal will be deleted, but the Appraiser Contact will still be in Contacts.
Note:
Appraisal Tracking is only available on Collector and Organization plans.