how to install <Preempt-RT kernel> on top of Wheezy

Help please. Have successfully installed Debian Wheezy, now trying to install Preempt-RT kernel having already set up a root password during the Wheezy install. If not possible, how then do I edit so there is no root password??
When I wrote in Terminal <sudo apt-get update> it asked for my sudo user password which i do not have - I gave it my root password and it said it was wrong, which I assume is another way of saying sudo disabled (on account of having already set up a root password)?

Are you sure it is asking you for the psw as the first box that comes up it wants the user name and then the psw.

That has caught me out and probably others as well.

in linuxcnc.org/docs/html/getting-started/getting-linuxcnc.html, section 7.1.3, i am instructed to open Terminal and type in when i do that , it asks <[sudo] password for adam:> . I enter my root password and it says <adam is not in the sudoers file. This incident will be reported.>
What do i do to get into the sudoers file??

how do I reinstall?

Ok so i am simply rebooting from original wheezy netinst.iso

Success - all loaded and ready to play with. Thanks

Stormbird,

What did you do to get back up and going? Did you reinstall via live cd?

I just reloaded the netinst.iso file and followed the instructions on the linuxcnc website again , making sure to leave passwords blank where possible. It did not remove the first install but the latest install is at the top of the boot list so no problem (I do seem to have 4 different operating systems on the hard disc now - the top of the list being the amd64 version of Debian wheezy with Preempt-RT kernel). Have a very large hard disc so no problem but would be nice to know how to delete the other 3