How to create a different instacne and how to initalize these different instances

hi

How to create many instance in the informix DB and what are the Configuration files needed to be changed

For Example

Assume that i am having an onconfig.server1 as

SERVERNUM 9
DBSERVERNAME server1
DBSERVERALIASES

And onconfig.server2 as

SERVERNUM 15
DBSERVERNAME server2
DBSERVERALIASES

In this Case what are the changes we have to do for the Environment file

Now in the envoronment file it is pointing to onconfig.server1 & sqlhost.server1

If iam creating one more instance how can i modify these files
Could you Please give us some technical solutions

Thanks
karthik