I'm not sure this is something you can do while running on the root volume.
The easiest route (or the route I'd take) will probably be to boot to rescue media, activate the VolumeGroup, force fsck /dev/VolGroup00/LogVol00, resize2fs to the reduced size you want, lvreduce the LogicalVolume.
Keep in mind that if you reduce it too much (smaller than you have data consumption) you'll run into problems. also, you don't want to reduce the LV smaller than the filesystem. I usually fudge an extent or two just to be safe.
May not be a bad idea to have a backup of anything you want to keep ahead of time... just in case.
If all goes well, then you reboot successfully and use the reclaimed extents for whatever other Logical Volume(s) you want.