Canon PowerShot SX400 IS Black Manual (en)

Erasing Multiple Images at Once
You can choose multiple images to erase at once. Be careful when 
erasing images, because they cannot be recovered. However, 
protected images (
Choosing a Selection Method
Access the setting screen.
Press the [
] button, and 
then choose [Erase] on the [
tab (
Choose a selection method.
Press the [
] buttons to 
choose a selection method, and 
then press the [
] button.
To return to the menu screen, 
press the [
] button.