I can't delete a transformation because it is used too heavily

Deleting a transformation from the Transformations center or the Admin API will trigger the deletion of all the derived assets associated with this transformation. You will receive the following error:

Error 403: Unable to delete transformation because it has too many derived resources

Due to the nontriviality of deleting a large number of assets and invalidating the cache copies at the CDN level, this operation can only be performed for transformations with up to 1000 derived assets associated with them. 

Named transformations already associated with many derived assets are also protected from being updated.

If you still need to delete a transformation, we have a support article that provides all the instructions on how to delete the derived resources: https://support.cloudinary.com/hc/en-us/articles/202521072-How-to-delete-derived-resources