Basically the wiki at summercode.com says it all, go to (or wget) the latest version at http://www.scala-lang.org/download and untar it. Then move the folder to /usr/share/scala. Then link the address of the new binaries to the old binaries in /usr/bin. The main problem here is that you have to delete them first so I just want to add this little piece of shellscript(including the instructions from the tutorial mentioned above):

$ wget http://www.scala-lang.org/files/archive/scala-2.10.3.tgz
$ tar zxf scala-2.10.3.tgz
$ sudo mv scala-2.10.3 /usr/share/scalasudo rm /usr/bin/scala
$ sudo rm /usr/bin/scalac
$ sudo rm /usr/bin/fsc
$ sudo rm /usr/bin/sbaz
$ sudo rm /usr/bin/sbaz-setup
$ sudo rm /usr/bin/scaladoc
$ sudo rm /usr/bin/scalap
$ sudo ln -s /usr/share/scala/bin/scala /usr/bin/scala
$ sudo ln -s /usr/share/scala/bin/scalac /usr/bin/scalac
$ sudo ln -s /usr/share/scala/bin/fsc /usr/bin/fsc
$ sudo ln -s /usr/share/scala/bin/sbaz /usr/bin/sbaz
$ sudo ln -s /usr/share/scala/bin/sbaz-setup /usr/bin/sbaz-setup
$ sudo ln -s /usr/share/scala/bin/scaladoc /usr/bin/scaladoc
$ sudo ln -s /usr/share/scala/bin/scalap /usr/bin/scalap

Or download the file here: update-scala.sh (github clone)