How do I make a user account the local administrator

I was having a lot of problems with my desktop, so a friend suggested I create a new user account and delete the old one. Sounded simple to me. I created a new account, set it as administrative, and thought everything was working fine so I deleted original user account which apparently was the local administrator. Now when I try to download certain programs I get a message saying must download from administrative user. But my account is set at administrative. Help, please.