You need to select all the images that you want to delete by holding CTRL + Click in Windows and Command + Click on Mac.
Once done, you can press the delete button to remove it from the catalog.
It will also provide you the option to delete it from the computer as well.
Please click on the below link for detailed informationi.
Hope this helps.
First you have to Define which ones you want to keep and which ones you want to delete. There are several ways to do that. Google is your friend.
Big help thank you.
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