i download some new themes on my blackerry 7520. after i did it the new themes wont work and i cant get my original theme back. can someone please help?

ok i found a thread about getting a javaloader to wipe my black berry and restoring my software. the directions it gave were not clear because i could not find a javaloader program from blackberry. so, can someone tell me the name of the programs and give me directions. thanx