Sure: when you've made a new one, just go into your gallery, select "edit icon details," and upload the new piece. It keeps you from having to submit it again and then get in trouble for redundancies.

Thanks for the comment, yeah I only just noticed that the trunk isn't really shaded enough. Is there any way I can change the image? (on the site that is)

the colours in the trunk of the mushroom have almost zero contrast- and while you have a light source on the cap of the mushroom that lgihtsource doens't seem to affect the trunk.  There needs to be a shadow from the cap on the trunk.

I suggest making you canvas bigger too, give the mushroom some room to breath.