1 : Use Rename.pkg(I tried to use this but after using this app for 3/4 times all applications in sd were vanished from app launcher,cant change app's icon)

2 : B4 installing any jar files (use winRAR) open META-INF\MANIFEST.MF usin wordpad to change MIDlet-name this will change app name b4 installation changin icon is not easily possible here

3 : This is most reliable method to use but b4 proceedin pls mke hidden files visible & backup ur .system folder

STEPS :
1 - goto .system\java open CardRegistry usin wordpad (there might b 3 files having name CardRegistry but select file havin file type : File)
2 - now rename the req apps
3 - save & close this file
4 - now renaming is done
5 - to change icon goto the folder of app (java or QTDownLoad for mpkg app)which u want to edit & replace the existin icon file with new file havin same name & extn (select res of this file abt 64*64 or less)
6 - ur icon is changed now
(NOTE : to change icon to an icon havin diff extn u hav to edit CardRegistry aswell )

TIP : defragment ur sd card as req which'll enable sd card to store data in contagious mem locn & it might boostup speed of execution,also free memory will b available in continuous blocks