Go Start->Settings, tap the System tab at the bottom, and tap Memory. On the Main tab it will show you a breakdown of memory, including how much is free, how much is used, and what it's allotted for...programs or storage.
If most of the memory is for storage, tap "Find large files using storage memory" at the bottom, then move any you can (particularly audio and video files) onto your storage card to save space.
If most of the memory is for programs, find out what's running by tapping the Running Programs tab. From there stop any/all programs you don't need running, including ActiveSync.
Go back to the Main tab and adjust the slider as appropriate. Remember, RAM is used for storage (including PIM data such as addresses, calendar, etc) and for running programs under Windows Mobile 2003 SE (CE 4.2). In WM5.0 Microsoft used RAM only for running programs, moving all storage into ROM. This is good for two reasons. First, data stored in RAM will be lost if the battery dies, whereas it won't if it's stored in ROM. Also, RAM is better served for running programs, enabling you to multitask and run memory-intensive programs...if it's split for storage as well it won't do as well.
Finally, note that tapping the 'X' does not truly close out of most programs, but instead minimizes them. Thus, they are still running in the background, taking up memory. To solve this problem, I recommend the free program Magic Button, which will make the close button actually close the program.
Hope this helps,
My Ipaq has 64 MD of RAM but consistently I am only getting 3-9 MB of Ram to run Programs. I use the unit as my GPS so when it fails...its not a good thing. I have 2 GB of expansion memory split over 2 expansion cards, one CF and SD and have moved as many of the programs to the cards as possible. Does anyone know what could be the memory HOG? Thanks in advance!