Way too big.
I just did some test and it needs to be smaller than 0.99 Mb or 2050x2729 pixels.
If you are unsure of how to resize your pictures open the picture with the Paint program on your computer. Or when the picture is open right click it and click "open with paint" Then in the toolbar you will see the "resize" option. Click on that, then at the top it will give you two options percentage is the default one but there is another box for pixels. If you click on pixels then change the size to smaller than 2050 pixels and then click OK. Then you will need to click on file and then "save as jpeg file" Then it will save it to somewhere on your computer. Then just use this picture for either a full size picture in your post or as a attachment.