There's no "proper" way to do this right, really. I suggest you backup your data and do a full reformat.

Alternatively, you could: 1) defragment the data partition (assuming this is the last one on the hdd), 2) resize the data partition using HDConfig and create a hfs+ partition to cover the gained space (be extra cautious here, the partition must stay larger than the amount of data you had on it!, I'd say 20% is a safe margin), 3) save the new layout and reboot, 4) launch SFSDoctor and repair the data partition, 5) install OSX on the new partition, do NOT attempt partitioning on OSX!