I once took my personal iMac to work and enterprise policy settings have been downloaded unto it. I am trying to download the OS X EL Capitan beta and I keep getting the software update policy on the mac will not allow it. I would like to disable this setting as it is my private mac, but I have no idea how to or where to do it.
Administrators use Configuration Profiles in Mac OS X to standardize settings & behaviour.
A configuration profile can contain settings for configuring a user’s Mail account, Wi-Fi settings, VPN settings, and more.
To view installed configuration profiles
As you said this is your personal computer. Assuming you didn't do anything of this sort, you should be good to remove all the profiles listed & restart the computer to bring the changes in effect