You have lost admin access to your system. That occasionally happens after upgrading your system.
The result is that you don't have any admin rights. You have to use admin rights to get admin rights back.
Well, how does one do that? It quickly becomes a circular path to nowhere....
So, the easy path back is to re-enable the system account setup assistant (that tool runs when you first set up a new Mac.)
If you can get that to run, you can simply make a new account, which is, by default, an admin account.
Then you boot to that new account, which will then allow you to change each still existing accounts, or just one, to an admin user. Log back out, taking you to a login screen. Log back in to your normal user account, then delete the new account that you just created, if you want to do that. And, you are back in the "admin" account business.
Here's a page that shows you how to so all that:
http://www.theinstructional.com/guides/how-to-re-run-the-os-x-setup-assistant