IMac :: How To Reset OS X 9.2 Password

basically i have an old imac computer which doesnt come up with cd and i forgot the password, I have read some tutorial that tells how to reset the password by:

holding down the command +s key when we hear the tone of imac at the startup and then insert some command line.

The issue with me is that i tried it in mnay ways but i cant get to the terminaleverytime at the startup i use apple+s key ,nothing happens ,it loads normally and gets to the login screen, keys seems to be fine what can be the issue and is it there any way to get to the terminal w/o having cd etc.