first you need a bittorrent program to begin with, you can search for that on the web... Ok for extention changing
1) open up control panel (doesn't really matter, were looking for "Tool" menu up top).
2) Click on Tool menu option
3) Go down to Folder Options
4) Select the View tab
5) Uncheck the box that says "Hide known file extentions"
6) click apply, then click Ok
7) Right mouse click the downloaded file and select Rename from the options list that comes up
8) take the .jpg off and leave the rest of the file name intact
Then just double click it after you have a bittorent program installed on your PC and it will start downloading. ^^