Googled a bit, and created this:
Set fld="D:\Bos\Data\Graphics\Skins"
Rem 4K is 16777344, so a bit less.
Set FSize=16777340
Rem Show the files within this selection
@ForFiles /P %fld% /S /C "Cmd /C If @IsDir==FALSE If @FSize LEq %FSize% echo @FSize0x09@Path"
Pause
Rem Delete the files within this selection
@ForFiles /P %fld% /S /C "Cmd /C If @IsDir==FALSE If @FSize LEq %FSize% Del @Path"
1. Copy/paste the text into notepad, save as a .cmd file (Yeah, you know)
2. Set your skins folder in the first line, this one is mine.
3. Run it. It will show all skins smaller than 4K. It will then wait for a key press. If you press the key, the files listed will be deleted! If you do not want that to happen, hit Ctrl-C
Edit: Note that this one does it recursively, so it includes all sub-folders as well.
Tested this on my Pc, works. Very handy that ChkSkins is there, the 14 skins I deleted this way, were easily downloaded again... it's cool!