On Ubuntu 13.10, the default version of llvm is llvm-3.2. But you can install other versions of llvm (llvm-3.3 or llvm-3.4) through apt-get. However, the command line tools of llvm such as llvm-as, llvm-dis, llvm-link lli, llc and opt still point to the default version.  To use llvm-3.3 llvm-as, you must specify the version number as in

llvm-as-3.3

This is cumbersome. Fortunately, you can change the default version using update-alternatives. For example, to make llvm-link point to llvm-link-3.3,

sudo update-alternatives –install /usr/bin/llvm-link llvm-link /usr/bin/llvm-link-3.3 33

You can do this for llvm-config, llvm-as, llvm-dis, lli, llc and opt as well.