It’s in the README (I’ve included the appropriate section here)
5b FOR UPGRADING: (Within the RT 3.x series)
Read through the UPGRADING document included in this distribution.
It may contain important instructions which will help you upgrade
As root, type:
This will build new binaries, config files and libraries without
overwriting your RT database.
You may also need to update RT's database. To find out, type:
For each item in that directory whose name is greater than
your previously installed RT version, run:
/opt/rt3/sbin/rt-setup-database --action schema \
/opt/rt3/sbin/rt-setup-database --action acl \
/opt/rt3/sbin/rt-setup-database --action insert \