To set the resampled pixel dimensions, it is simply a matter of entering the desired size,
in pixels, for the side of the image (height or width) that you want to be the determining one.

In this example the longer side (width, in this case) has been set at 800 pixels, to keep within the optimal size as uploaded to PBase galleries
for on-line viewing. The other dimension (height) has adjusted itself automatically to keep the original aspect ratio (proportions) of the image.

Notice that the Resolution figure has not changed, and this gives an obvious clue to the fact that a re-sample has been specified.
Notice also that the overall image file size (1.55 MB) will be drastically reduced, reflecting the much smaller total pixel count.
This figure looks quite large, but it does not account for image compression, such as JPEG, in the file as it will be finally saved