diff --git a/src/lerobot/datasets/lerobot_dataset.py b/src/lerobot/datasets/lerobot_dataset.py
index c4686f968..9036827fa 100644
--- a/src/lerobot/datasets/lerobot_dataset.py
+++ b/src/lerobot/datasets/lerobot_dataset.py
@@ -14,6 +14,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import contextlib
+import gc
 import logging
 import shutil
 import tempfile
@@ -314,6 +315,13 @@ class LeRobotDatasetMetadata:
         # Update the Hugging Face dataset by reloading it.
         # This process should be fast because only the latest Parquet file has been modified.
         # Therefore, only this file needs to be converted to PyArrow; the rest is loaded from the PyArrow memory-mapped cache.
+        
+        # Explicitly delete old dataset to free memory before reloading
+        if hasattr(self, 'episodes') and self.episodes is not None:
+            del self.episodes
+            self.episodes = None
+            gc.collect()  
+        
         self.episodes = load_episodes(self.root)
 
     def save_episode(
@@ -451,7 +459,7 @@ class LeRobotDataset(torch.utils.data.Dataset):
         root: str | Path | None = None,
         episodes: list[int] | None = None,
         image_transforms: Callable | None = None,
-        delta_timestamps: dict[list[float]] | None = None,
+        delta_timestamps: dict[str, list[float]] | None = None,
         tolerance_s: float = 1e-4,
         revision: str | None = None,
         force_cache_sync: bool = False,
@@ -1051,6 +1059,13 @@ class LeRobotDataset(torch.utils.data.Dataset):
         # Update the Hugging Face dataset by reloading it.
         # This process should be fast because only the latest Parquet file has been modified.
         # Therefore, only this file needs to be converted to PyArrow; the rest is loaded from the PyArrow memory-mapped cache.
+        
+        # Explicitly delete old dataset to free memory before reloading
+        if hasattr(self, 'hf_dataset') and self.hf_dataset is not None:
+            del self.hf_dataset
+            self.hf_dataset = None
+            gc.collect()
+        
         self.hf_dataset = self.load_hf_dataset()
 
         metadata = {
@@ -1216,7 +1231,7 @@ class MultiLeRobotDataset(torch.utils.data.Dataset):
         root: str | Path | None = None,
         episodes: dict | None = None,
         image_transforms: Callable | None = None,
-        delta_timestamps: dict[list[float]] | None = None,
+        delta_timestamps: dict[str, list[float]] | None = None,
         tolerances_s: dict | None = None,
         download_videos: bool = True,
         video_backend: str | None = None,