To find the items you listed, go to Marketplace and then click on that navigation on My Items.
Here you can find a list of all the items you listed.
You can Edit/Manage or Delete your items here.
Click on Edit and find the edit items tool box:
Here click on Edit Item Photo and upload the new photo or delete the existing one.
You can also change/set a new Thumbnail. Click on Edit Thumbnail by move the small field in the picture to where you want it, then click on Save Photo: