I need to put new products on magento product pages and remove old ones. I have tried that on admin page but the old products don't delete when I try to.
The better way will be mass uploading. Collect all images in a folder and make a csv file with sku and related image path.
Upload image in
media/import folder and then import the csv file in
System > Import/Export > Import
You can get tutorials for mass uploading products in magento.
Images will be replaced by this method.