The XNAT 1.8.2 release offers a key configuration update in response to the Apache Tomcat 7 end of life announcement, as well as several bugfixes and improvements:
You can read the XNAT 1.8.2 Release Notes for more details.
Upgrading is (fairly) easy!
The upgrade path from XNAT 1.8 to XNAT 1.8.2 is as easy as configuring your war file for the version of Tomcat you're running and dropping the new war file in place. Upgrading from the XNAT 1.7.x line is only mildly more arduous. See the XNAT Upgrade Instructions.
XNAT Release Notes | XNAT Documentation