How do I put my macbook back into case-insensitive?

Recently wiped my macbook due to a virus, and apparently I wasn't reading things clearly because I managed to end up in 'case-sensitive' mode [mode?] which evidently means I cannot install League of Legends.

Please, someone, tell me how to fix this... Hoping I won't have to repeat the wipeout and start again... it was a tad inconvenient. [took three and a half hours to reinstall Mavericks last time]