I am unsure precisely where the file will be in AIX, but in Ubuntu/Mint there is a file at /etc/apache2/conf.d/security that has a directive ServerTokens. Change to your liking and restart Apache. 'Minimal' appears to be what you're after. 'Prod' will return only "Apache".
# This directive configures what you return as the Server HTTP response
# Header. The default is 'Full' which sends information about the OS-Type
# and compiled in modules.
# Set to one of: Full | OS | Minimal | Minor | Major | Prod
# where Full conveys the most information, and Prod the least.