have u tried hard reset first? it just flashes..basically you want th phone to be restored to its original settings...
Nokia C6 Hard Reset through button combination.
1). Turn the Nokia C6 OFF
2). Pull out the battery and reinsert it back again, then Power it ON whilst Simultaneously pressing and holding *+3+Call Button (green/ok button)
better get someone to help you out.....keep trying if u faill u ill know it has worked when it comes to the screen where it asks u to choose country....
no need for flashing
but if u insist on flashing just get good internet and use navifirm to download flash files.or update thru nokia suite