please don't make multiple threads, as it splits effort. For anyone else, the alternative thread has some answers too: viewtopic.php?f=33&t=30443
As this thread seems to be slightly different, I'll answer here too: I did exactly this. My data was on an ext3 partition, which I shrunk to size, created a new ext4 partition, then copied all the files over from the ext3 to the new ext4. It worked fine, but took ages. It's technically possible to do this with system files too, but I recommend taking a backup of the list of installed packages with dpkg --getselections and doing a fresh install (selecting ext4 as the format), then applying them again afterwards. You're much less likely to run into problems this way.
If you have a question that has been answered and solved, then please edit your original post and put a [SOLVED] at the end of your subject header
Hint - use a google search including the search term site:forums.linuxmint.com