i hope i can help
1- open the jar file on your pc with winrar
2- go to the folder META-INF
3- open the file MANIFEST.ME using any editor
4-ADD THIS LINE TO IT : " MIDlet-Touch-Support: true " (WITHOUT QUOTES )(in the first line for example)
5- save the file by pressing Ctlr +S on your keyboard then winrar asks you update archive
you say yes and here you go you just made your app full screen.
6- enjoy.