Can't put my accont as administrator

like the title say i am having trouble putting my accont as administrator.

I got the PC via a school program and since I finish my schoolarity I needed to create a personal accont which i didn't put as administrator and now i can't download anythng because when i try it ask for the user name and password of the admin acont things that i can't get.

any help would be greatly apreciated

(sorry if i made speeling mistake english is not my first language).