Q.How do I re-size my images?
A.The most effective way to save images for use on line, with relatively small file sizes that still retain a decent quality level, is by using Photoshop's "Save For Web" function.

Make sure the images are the correct dimensions first; under the Image menu go to "Image Size" and reduce to 72pixels/inch with the "Resample Image" option unselected - hit ok and the window will close. Go back in to resize the pixel dimensions to 432 (this time with "Resample Image" option selected).

Under the File menu go to "Save For Web". To the right of the new window that opens choose "JPEG High" from the list of presets. You should see how this affects the actual image in the preview and also the file size below. In this instance it still keeps the image quality quite high at around 60 - although the file size should now be reduced significantly. You can always try reducing this slightly for a smaller file size, as well as some of the other options, such as Progressive jpeg, etc. It's worth looking at the various presets here - and also opting to view 4 previews of your image so you can compare how each affects your image.