.net password/account reset

Hello,
I am having an issue with my computer and the .net account/password. The computer I have at home was purchased from a company that was overstocked with computers. Since then I have had no problem with the computer besides the account that it was set up on. There is a constant window that pops up asking for a password to be entered in order to view certain things and or to save the info (something to that effect).

Also it is the same password that involves trying to apply control settings on the Control Panel under Internet Options. I want to change the settings so that my children are unable to view certain websites but am unable to do so without that .net password.

If you could give me any information as to how I would reset that accont or change the password, I would really appreciate it.

Thanks!