I had a similar MP4 player which was claimed by the seller to be 16 GB but in reality was only 2 GB. I used this method
ChkFlsh method (revised) . In my hands it worked perfectly well and now the player is 2GB and error free according to h2testw scanning. It might not work on all players, but on the one I bought from urqiqiexpress on Ebay. When I just checked on Ebay, it says "no longer a registered user", so most likely the change name and appear as a "new business".