Re-foramting Hard drive

Well I bought a hard drive, that was meant for windows a while back, and as I was going to use it for both windows and mac I got it formatted for both.

Now i'm running out of space on the mac side, and I'm wanting to make it 100% for mac (move the pc side to another drive) but if I do this, will I also lose the media on the mac side?

I wold rather keep my projects in one pace (not move it) if I can because I am afraid I will make a big mess for FCP.

You need to backup the drive and reformat it. Disk Utility will wipe out all data. But it is pretty simple. Just copy the "Final Cut Events", "Final Cut Projects", and if you have one the "Final Cut Archives" folders. Format the drive, copy them back. No big deal. Just delete the backups when you're done with them.

I'm not aware of any app that will reformat a dual formatted drive without wiping out data.