My blackberry 8830 giving prob?

Press the ALT and CAP and DELETE keys at same times and let the Blackberry reboot. Test the blackberry performance and if it is still "frozen" or performance is slow, proceed to the next step. Locate the reset button hole on the bottom, back or under the battery cover of the blackberry device. Place the end of a pin or a paper clip into the hole and press the button. Let the blackberry reboot and test to confirm that the blackberry is no longer frozen and that performance is acceptable

The obvious answer is to clear the memory by getting rid of apps and other stuff which you don't need. Delete all messages which you have read and download any photos and other data to your PC. If you still don't have enough space, buy an 8Gb card, copy everything exactly as it is from the 4Gb card to the new one and replace the card.