Do you know that user cannot delete a customizable form template once it is used in the system?
But it is possible to delete it after all objects’ templates will be changed to another one.
To delete a template in use, open one by one all sources/materials/aliquots/tests for which the template is used or using batch edit possibility (select from the grid all necessary elements), edit the Customizable Form Template field to select Default or other template.
Once this is completed, the Customizable template could be considered as not be used be any objects and can be deleted.
Remember, once template is deleted, the template cannot be recovered/used again.