how can i remove apps preloaded on lg optimus 3d
Without rooting the phone you can't.
Yup you will have to root the phone and then use a program like 'root uninstaller' - definitely back everything up first though if you go this path.
Root your phone
Install Titanium backup
you can backup and uninstall any program you want. Be careful whille uninstalling program and dont uninstall any system related programs
Before uninstalling an app that's on the system first use the freeze option in Titanium Backup. If after freezing the app one or more system processes start to crash, or you get a lot of force closure issues, unfreeze and do not delete.
If after freezing the app and you have opened and closed a few system apps (Gallery, Google Maps, etc) and everything still worked, delete if you want to.
Separate names with a comma.