To resize your hi-resolution images to upload to display on the internet you need to resize your images.
With the image open go to Image/Size. Below you can see that this image is 1680 by 1080 pixels. It’s resolution is 300 pixels per inch and its physical dimensions are 5.4 by 3.6 inches.
Make sure that you uncheck Resample Image and set the Resolution to 72 pixels/inch. 72DPI is the resolution of a computer monitor. You can see that you Pixel Dimensions have not changed, but you can see that changing the resolution to 72 has changed the Document Size to 22.5 by 15 inches.
Once you have adjusted the Resolution to 72, check the Resample Image button again and now change the Pixel Dimensions. Change the Width to 600 pixels. And you can see that now the new image will be 703.1 K as opposed to the 50.1 M the images used to be. Click OK.
Now that you have resized the image you can save it for the web. Go to File/Save for Web
A new prompt pops up, click on the tab 2-up, this will show the original image on the left and the optimized for web image on the right. Change the format to JPEG, and the Quality to 70 percent.
You will see at the bottom of the image that the original image is 703 K while the optimized image is 59.7K, even smaller than the resized image.
Below is the optimized image to display on the internet.