All you have to do is find the pic in your pics or douments ect files on your PC. Right clik on it and get the menu. Click "edit", follow all the prompts and from there you can click "resize" .
You have to type in 1024 for vertical and the horiz will adjust automatic. Sometimes you will have to rotate 90 deg there to get the 1024 vertical. Then clik save and follow the prompts. If you want to re-post the same pic here again you have to adjust the number slightly( EG change 1024 to 1000 ect) and this site will let it pass.