EOS 5D Mark IV: Free up card space

If you are running out of memory card space and need to free some up to continue shooting, you can use the protect image feature to make this easier. Instead of deleting images one by one, instead go through and Protect the images you wish to keep. Once the images are protected, you can use the Erase All images (NOT Format) to delete those images not protected. To make this process even faster, in the Yellow-3 menu tab, set the RATE button function option to ‘Protect’. Instead of having to go to the menu to protect each image, you will now be able to do it directly with the RATE button while viewing the image in playback.
Camera settings
EOS 5D Mark IV