A few simple things to increase your memory -- put all pictures, videos, ringtones, etc. on a media card so they are not taking up device memory.
Don't keep apps running in the background that you don't need. Taking out the battery every few days is a good idea, too.
Uninstall any apps that you don't use much or don't need.
And see here: http://www.blackberryforums.com/gene...ee-memory.html