Don't uninstall 5.14 modules. Don't mess with the default Perl because it's used by system processes. Set up (as you did) another dir for 5.18, and install the modules you need there. Then make sure your path to perl -- hashbang and lib directives -- point to the new package.

Search this site (Google works well for this) for some combination of keywords "ubuntu," "update," "Perl" and "version."