UGh. I was brief before for a reason
To login as an admin you start your computer (or reboot if started) and at the login screen, hit ctrl-alt-del (twice I think) and you'll get a "real" login prompt. You may have alread given yourself admin rights in your normal account when you setup the PC *so this may not be necessary*. If you can install programs under your login, then you prolly have admin already.
As for ownership and permissions...hehe RTFM:
Goto windows help and do a search for "take ownership". Take a look at the 2nd and 3rd articles that come up.