Bypass administrator password on imac?

Help! I just bought a used Apple iMAC it's beautiful. Its the one that has a large screen with everything built in to it- no separate tower- thing Is it has administrator acct. With a password and guest acct. Lets me in but not run any programs without administrator password bypass the i administ clear out everything and do a factor clear out everything and do a factory restart kinda like on iPhone?

There are a few ways to do this, but the easiest way would be to use the discs that came with the computer and perform what is called and erase and install. This will bring the computer back to factory defaults and erase any of the existing data on the machine, including any passwords. Your nearest Apple store also has these discs if they weren't given to you when you bought the machine.

If you don't have an Apple store nearby, the best way would be to hack in to the machine by shutting it down all the way, turning it back on while holding Command (the clover leaf looking button to the left of the spacebar) and the letter S at the same time until a black screen appears. Wait a minute or so until everything has finished loading and type the following exactly:

mount -uw /
passwd root

The computer will then ask you to enter a password, but as you type it won't appear to be doing anything, rest assured it knows what you are typing. Use a password that is easy to remember, confirm the password by typing it again when it asks, and then type the word reboot and hit return. Once the computer reboots there will be a new option for Other Accounts, click on that and then in the user name field type root and the password will be the password you typed earlier. From here you can delete the old admin account and create your own. I highly suggest that you do not use the root account for any other purpose however, and instead use a regular admin account as the root account has very little built in security compared to an admin account.