Well... LVM is not a filesystem, is a Logical Volume, a method of allocating space on storage devices. Maybe you have more disks/partitions joined in a single Volume. In that case you have first to unmount the volume, remove it and then re-format the disk/partition using gparted (I assume you already know that this will destroy any data on the LVM).
Just out of curiosity, which is the output from fdisk -l and df -k and pvscan? These will tell you about the real and the logical volumes existing on your machine.
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