Hello Palamed. You can go to your game history on Chess.com and then click to actually "view" one of your completed games and then you can click "get PGN" when you should see a new window pop up to get the actual PGN of the game.
Then once you have the PGN of the game you can use the Chess.com diagram editor tool ---> http://support.chess.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=91
Just to clarify, when you "view" your game, the data sub-window will probably appear with the "Messages" tab activated. You'll need to click on the "Moves" tab in order to be presented with the "Get PGN" button. Clicking on that will download your PGN.
Depending on how you have your browser set up, the PGN might download directly to your default download directory, or you might first be presented with a download window where you can specify which directory you want to use on your hard drive for the download target.
--Cystem
How do i post online game here? I tried to download pgn,but nothing happened,meaning that i dont know if it were downloaded and where