Simpler way, if you have access to the server:

Linux: /opt/TeamCity/bin/version.sh (change the path to installation directory, if needed)

Windows: \TeamCity\bin\version.bat (again - change the path if needed)

It will display something like:

Using CATALINA_BASE: /opt/TeamCity

Using CATALINA_HOME: /opt/TeamCity

Using CATALINA_TMPDIR: /opt/TeamCity/temp

Using JRE_HOME: /usr

Using CLASSPATH: /opt/TeamCity/bin/bootstrap.jar:/opt/TeamCity/bin/tomcat-juli.jar

Server version: Apache Tomcat/7.0.59

Server built: Jan 28 2015 15:51:10 UTC

Server number: 7.0.59.0

OS Name: Linux

OS Version: 2.6.32-573.22.1.el6.x86_64

Architecture: amd64

JVM Version: 1.8.0_191-b12

JVM Vendor: Oracle Corporation