On the other hand, it does not change much to resize them when replacing them or before, as the site remembers when you check the "resize" box in this case they can be resized when put on the site.
But indeed for the next time it would be better to resize before saving to jpeg.
Also, there is a thin black border (at least on some). Maybe not a problem this time, but again to avoid as it reduces the quality of the image on borders due to jpeg algorithm (so has to be removed before jpeg conversion).