First thing to do is see what applications are running the in background. Hold down the BlackBerry button and a small retangle box will appear showing the applications that are currently in use. Some of the apps are always running: Phone, BB Messenger (if installed), Home, Browser, and Messages. If other apps you are not using are still running, close them. See if that helps open up some memory.

Many believe just exiting an app closes it. However, if you don't close/exit from apps such as viigo or ScoreMobile your memory is going to be eaten up by them.