best thing would be to download the images and resize them. If you are on a pc it is pretty simply open them in paint and then click on the resize button in the top bar and change the size to pixels (600- 800 px ) should sit nicely on your page. Just do a couple and see. Also make sure you save a jpeg over png as the size will be smaller.
Another thing you can do is add a plugin called https://wordpress.org/plugins/wp-smushit/ it will Compression and Optimization your images. Just use the free version no need to get pro version.
Hope this helps 🙂
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