how to update existing dataset

documentation/dataset_conversion.md

@@ -25,7 +25,7 @@ Within each task folder, the following structure is expected:
     ├── (imagesTs)
     └── labelsTr
 
-**Please make your custom task ids start at 100 to ensure that there will be no conflicts with downloaded pretrained models!!!**
+**Please make your custom task ids start at 500 to ensure that there will be no conflicts with downloaded pretrained models!!! (IDs cannot exceed 999)**
 
 imagesTr contains the images belonging to the training cases. nnU-Net will run pipeline configuration, training with 
 cross-validation, as well as finding postprocesing and the best ensemble on this data. imagesTs (optional) contains the 
@@ -195,6 +195,17 @@ See [here](../nnunet/dataset_conversion/Task120_Massachusetts_RoadSegm.py) for a
 This script contains a lot of comments and useful information. Also have a look 
 [here](../nnunet/dataset_conversion/Task089_Fluo-N2DH-SIM.py).
 
+## How to update an existing dataset
+When updating a dataset you not only need to change the data located in `nnUNet_raw_data_base/nnUNet_raw_data`. Make 
+sure to also delete the whole (!) corresponding dataset in `nnUNet_raw_data_base/nnUNet_cropped_data`. nnU-Net will not 
+repeat the cropping (and thus will not update your dataset) if the old files are still in nnUNet_cropped_data!
+
+The best way of updating an existing dataset is (**choose one**):
+- delete all data and models belonging to the old version of the dataset (nnUNet_preprocessed, corresponding results 
+  in RESULTS_FOLDER/nnUNet, nnUNet_cropped_data, nnUNet_raw_data), then update
+- (recommended) create the updated dataset from scratch using a new task ID **and** name
+
+
 ## How to convert other image formats to nifti
 Please have a look at the following tasks:
 - [Task120](../nnunet/dataset_conversion/Task120_Massachusetts_RoadSegm.py): 2D png images