first, install gparted; open a terminal and type
sudo apt-get install gparted
...It should be simple then. You just select the partition, right click, delete
but watch it!!! you should know that after you do that you'll have the 115 GB unallocated! that means that they're not part of any partition and you can't normally use them. Consider them as floating in the air or something and I really don't think you want that, do you? After deleting the partition you should then stick the unallocated space to another partition. That depends on how your hard disk looks like. You can take a screenshot of gparted and put it here to let us see your hard disk. You can also just follow the documentation here http://gparted.org/display-doc.php?name=moving-space-between-partitions .
...Just a friendly hint. If you don't really need to delete the partition and you can use it as it is then it's better not to play around with partitioning much because you might loose your data.