how can i delete admin account during bootup using cmd command in win 7?

i run cmd in Elevated Command Prompt mode.

i used commands such as;

net user administrator *    (but can not change password, the system error 5 has occured)

net user administrator /delete (access is denied)

net user administrator set /inactive

net user administrator /inactive:yes

but all these above not worked at all.

so plz, tell me how can i delete admin account if i have forgotten my password without using any disc but the cmd. thx