How can I know my database version?
If you follow this link there are several ways.
One of them shows you the architecture.

From that page: 

$ db2level
DB21085I  Instance "db2inst5" uses "64" bits and DB2 code release "SQL09071"
with level identifier "08020107".
Informational tokens are "DB2 v9.7.0.1", "s091114", "IP23034", and Fix Pack "1".
Product is installed at "/opt/ibm/db2/V9.7".