You can update art and preview by gitting the 'edit it' under the art to upload the revision.

The forum is there to help with feedback and questions and help as you learn how to pixel :)

Ah, my apology! I was rushing when posting this, so I didn't read the rules! I'm re-uploading it now, thanks for your information! =)

Hi and welcome on PJ 

There are a few elements that would need to be changed if you want your piece to make it to the gallery. 
Your submission has to be pure pixel art (quote from rule #6 in the "submit" menu: "Pixel art implies that each pixel is placed by hand (no filters, paintbrushes, gradient fills, etc)"). Since the background here is problematic, prefer a solid color background or transparency :)
Also, PJ provides an automatic zoom in/out tool so you don't need to resize your art. For the preview picture, you can use a cropped part of the original pic or make a specific one, but this too needs to be pixel art. 
For more ease, you can edit the piece or you can submit an other one and delete this one so there won't be duplicates.

Hope these elements will help you so that you won't be disappointed since this piece has few chances to be accepted as it is now