I have an older iMac that I want to change to my wife's use. I don't need to stay listed as user. Do I just change the Administration name and log on info? Will that affect my other 2 computers that are exclusively mine?

If the machine is remaining in the household and you just want to set it up for your wife's exclusive use, then I suggest you simply do this: create a new admin user account for your wife, then delete your old unneeded user account.

Start with Steps 1-4 of this Apple Support document:

https://support.apple.com/en-us/HT201065

Then, when you're confident that you're ready to set her up do this:

1. Be certain that you have backed up or transferred any files from your user account that you might need or wish to keep.
2. Log yourself in then go to System Preferences > Users & Groups. Unlock the panel and create a new user with Admin privileges. This will be your wife's user account. Assign the account a password.
3. Log yourself out of the machine and login to your wife's new account. Go back into System Preferences > Users & Groups. Unlock the panel and then delete the user account that was yours. You will be prompted to Save, Don't Change, or Delete the home folder. If you are content that you no longer require any of the files in your old user account then you can safely delete the home folder.

Your old account and associated data will be removed from the machine and your wife will now have her own unfettered access as an administrator of the iMac. And this will not affect anything on your other devices.

Done. Easy peasy.

see this link, it applies to what you are looking to do

Before you sell, give away, or trade in your Mac, you should back up your computer, disable some features and services, and restore to factory settings by erasing the hard drive and reinstalling macOS.

https://support.apple.com/en-us/HT201065