You can delete all the keyframes from selected layers, or simply delete one layer or multiple layers at a time. 
Note: You can select multiple layers at a time by Ctrl-clicking each one or by Shift-clicking a range of layers. 
To delete all keyframes from an animation layer:
- Select the layer or layers with keys you want to delete. 
 
- Right-click one of the selected layers, then select Clear Animation on Layer from the context menu. 
The layers no longer contain animation. 
  
To delete selected animation layers:
- Select the layer you want to delete. You can also Ctrl-click to select multiple layers. 
 
- Click the Delete button in the Animation Layer editor toolbar. 
You can also right-click on one of the selected layers and select Delete from the context menu. 
 All selected layers are removed from the scene.