How to uninstall the old perl versions ? and whereis @INC database ?

You can delete the old ones. However, once done, you need to ensure that you have all the perl modules you need, so:

rm -Rfv /home/.cpan/
/usr/local/cpanel/bin/checkperlmodules

Keep running checkperlmodules until it runs cleanly (i.e. no more module updates).

For good measure you may have to reinstalled exim too as it has some perl module dependencies:

/scripts/eximup --force