I highly recommend ditching the class 4 micro SD and purchasing a class 10 4GB to get more stability.
Does a 8GB micro SD work as well ? (That's the smallest I can get at my local store).
And is it just a matter of stopping the Titan, exchanging the SD card, and restarting it again? Or is there more to it?
Wasted space doesn't harm.
What is important is the
class of the SD card (read/write speed).
Look for Class 10.
Switching to another SDcard is the same procedure like your SDcard corrupted.
Prepare your new sdcard, shut down your miner, replace sdcard and restart.