I encourage you to read his post and mine, especially if you never looked at an AIX box.
I am posting Greg's text here, just in case.
The installation of Domino on AIX is fairly well documented, and one place to learn is from a posting by Keith Brooks. Before installing the new version of Domino, you will want to back up the existing install. An easy method is to use the tar command for this purpose. However, you will want to make sure that you have enough disk space for this file, probably about 600MB (more or less). To create the tar file, at a command prompt, type:
The v switch puts the command in verbose mode, so that you can see the files being added to the tar file.
Now, install the new version of Domino, following the steps outlined in, for example, Keith's post. Start your server, do your testing to confirm that mail is routing and any Domino add-ins are functioning properly. However, should you install, for example, 64-bit Domino 8.5 on AIX and find that some add-in does not work, you may be required to rollback to your previous version.
[Blog intermission - this is where you realize that operating systems like OS/400, AIX, Linux, and Solaris are really, really good].
Stop the Domino server. The Domino program files, for example, might be found in /opt/lotus/domino. Delete the domino folder. Change your directory to the location of the tar file that you created before you performed the upgrade. In that directory, type:
This command might look like this:
tar -xvf domino801.tar /opt/lotus
Once you have extracted the files from the tar, start the Domino server. You will see that you are now running the previous version. At this point, check the core Domino files, admin4, names, and events for the template versions. You may have to replace the design of those files to use the older version's templates.
Please note: the tar commands and Domino file structure may not be exact, but should provide enough information to assist you.