If you have a hacked phone, you can install MapDrive v1.01 and set
If it is not hacked, goto settings->application manager (v5) or applications->app. manager (v3) and try removing some programmes via app manager.
Best thing is just to backup messages, emails, notes and contacts using the PC and doing a hard-reset on the phone (*#7380).
Connecting it to the PC with Nokia PC suite ONLY lets you view C:\data.
I'd remove something and install x-plore and prune my C: with that.