Cleaning out rootfs and VolGroup-lv_root

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Hi,

Hoping someone can help me out a bit. I'm new to linux and am using the OS to run DNA sequence assembly software. After an overnight run I noticed that the program failed due to insufficient memory. A little internet reading and command prompt toying led me to this:

Filesystem                    Size  Used Avail Use% Mounted on
rootfs                         50G   48G     0 100% /
devtmpfs                       20G     0   20G   0% /dev
tmpfs                          20G  8.0K   20G   1% /dev/shm
/dev/mapper/VolGroup-lv_root   50G   48G     0 100% /
tmpfs                          20G   49M   20G   1% /run
tmpfs                          20G     0   20G   0% /sys/fs/cgroup
tmpfs                          20G     0   20G   0% /media
/dev/sdb3                     497M   96M  377M  21% /boot
/dev/mapper/VolGroup-lv_home  344G   36G  291G  12% /home

I did see another thread about this type of a problem but the responses seemed focused on finding the cause. In this case, I'm aware of the cause (Trinity RNA-Seq software max memory not set) but cannot figure out how to clear rootfs and VolGroup-lv_root.

Thanks in advance