Edit Speaks Messsenger.. How?

i ahve been trying for days now to edit the Sparks Messenger i have managed to figure out that .jar files are pretty much complressed .zip fiels are i can use Win Rar to open these fiels and well it gives me all the folders. I found a folder called images and i found the main sparks logo which is the logo when u first boot up the program it says it above were you put your username and password in, i edited it and put it back into the jar folder by deleteing the original and re openng the program it didnt work it still had the same old logo… what did i do so wrong?