Maybe your mom put time restrictions on the computer because you spend too much time on it. If it's the family computer (ie one in the home office or kitchen or whatever) then it's your parents decision what you can and can't do on that computer. If you don't like it then get an after school job and save up and buy your own laptop or desktop.

To answer your question, the only way I can think of removing time restrictions from your user is to wait until your mom, dad or whoever else is a Administrator on that computer to leave there user logged on and they've left the computer room. Then go through the control panel, to user accounts and there should be the option to remove time restrictions.