Ahh alright, lets get started!

After creating your track, you want it to relfect that in your thumbnail right? Then go get your pic that one want so badly to show up. On Windows, go to the directory "C:\Program Files (x86)\Steam\SteamApps\common\Chiptune Champion\misc". There, you shall find this pic right here
Move that somewhere else or delete it. Get that pic that you want to as your thumbnail and place it here. Now your not done yet, you still need to convert it to the *required* size, you must rescale it up or down. Right click on your pic and select edit, Paint should come up onto the screen. Right next to the Select icon is the resize button, click it. Click on "Pixels" and if it is not already, type in 512 in the Horizontal and Vertical boxes and click ok. Now click on file and then the arrow next to the "Save As" button. Click on PNG Picture and name it "workshop_image" make sure that the newly made pic is in the "C:\Program Files (x86)\Steam\SteamApps\common\Chiptune Champion\misc" directory. Now upload the pic using the in game editor. If you did everything here, it should have worked. I did this and I got my pic to show up on the workshop. This is the result:
Hope this helps people out!