i would install the new version parallel to the old. so you're safe in the way that you have the running version in case you need it.
then you can either link the new executables to /usr/bin/perl* (or such) and let the old version be callable through perlx.y.z, or let the old version be the default.
that depends on how many users and scripts there are relying on perl, so go and ask before changing anything.
infos on changes are found in perldelta.
update: and, of course, be sure to get a stable version.