Set Your New Administrator Password Without Knowing Older Password.

If you forget your old password or any other reason and want to change your administrator password then follow these steps

Go to Control Panel >> Administrative tools >> Computer management >> Then System Tools

After That Go to Local user and Groups >> User

Then  on Administrator Do Right Click and then Set Password >> Then Click Proceed  

Now enter your new password and press ok button.

I hope it is helpful for you to solve your problem.