Help needed to load new programs to Diamond

[nmoreman]

I have a question about what I have done, have been researching and one answer you gave needs more explanation to me.
I have Memory, I am really eating up Main Storage and don't know if I am loading incorrectly.
Basically I have 8 mb's left, have less than 2 dozen pics, 8 ringtones, and a few programs, such as Google Maps, 5 apps form Cab's.
When it asks where do I want to load it, should this be to device or internal storage.
Running Sprint standard phone programs.