How to convert a EXT3 partition to EXT4 without reformatting

# tune2fs -O extents,uninit_bg,dir_index <span style="color: #ff0000;">/dev/sdXx</span>

# fsck -pf <span style="color: #ff0000;">/dev/sdXx</span>

Then, make sure to change to ext4 any entries in /etc/fstab