How do I delete Administrator in Users & Groups

What to do before selling or giving away your Mac - Apple Support

Since 10.7, OS X is only licensed to be transferred to a different owner if it originally came with the computer when it was new. Transferring a copy of OS X that you obtained from the Mac App Store is not allowed.

You can reinstall the original OS that your Mac came with by using Internet Recovery, or if it came with system restore DVDs, by booting from those. This will solve the problem you were asking about and will make the computer all ready for the new owner, who can download and install El Capitan himself for free if he wishes.

help2233 wrote:

I deauthorized iTunes but really don't want to reformat my computer if there is a way of either signing myself out as a user and/or removing myself. Possible?

Even ignoring the EULA requirements for a reinstallation for the moment, consider that your family member will now have whatever customizations and add-ons and tweaks and tools that are installed, and this can lead to confusion and weirdness, and can lead to apps and tools that are configured for or that are licensed to you or other folks. It's a whole lot easier for everybody involved to either start with the family member's existing OS X backups and migrate those to the "new" system, or to wipe the system and reinstall OS X — as the EULA expects — and start with a generic and fresh installation.