If you've been running Linux for a while, you're probably using the now slightly outdated EXT2 or EXT3 file system. Technology blog Ghacks has a guide to converting those formats to the newer, faster EXT4 without doing a clean install.
While many of us prefer to do a reformat every year or two, if you don't feel like reorganising all your data but would like the speed and stability of EXT4, you can convert your file system without losing your data. That said, you'll of course want to back everything up before doing this — just because you shouldn't lose your data doesn't mean something can't go wrong. It's fairly simple if you're comfortable with the Terminal, which, if you've been a Linux user that long, is pretty likely. Hit the link for the full guide.
Convert ext2/3 to ext4 [Ghacks]