1. Go to My computer -> Tools -> Folder Options


http://img137.imageshack.us/img137/34/46164566un1.jpg


2. Select Tab "View" and there uncheck "Hide extensions for known file types" after that press "OK"


http://img266.imageshack.us/img266/2250/44485202kr2.jpg


3. Now, go to the game file -> Right Click and "Rename"


http://img84.imageshack.us/img84/447/36591873yx0.jpg



4. From .rar, .zip to .jar and DONE


http://img225.imageshack.us/img225/465/94173937cd7.jpg

http://img88.imageshack.us/img88/2064/53556320up7.jpg