How to replace Exim with Postfix question

[Admin]

OK, I know I did something wrong here. I downloaded, compiled and installed 
(I Thought) Postfix, and I THOUGHT it became my default MTA but evidently 
not.

I am running Centos 4.7 with cPanel., and I know this can be done, since I 
used to run a dedi that had that setup.

If any one would be so kind as to point me to a step by step install/replace 
guide I would appreciate it. It may be I looked at it on Postfix's site but 
my old eyes don't always see what they should, and I may have very well 
missed it. Someone I know suggested that I need to replace the sendmail 
binaries, but didn't leave any ideas on that

Thanks

Larry