During competition the switching between the two program is done by the field management software. All your team needs to do is to start the auto-op program you have and place your robot on the field. After auto-op is finish, field management software will start your tele-op for you. Just make sure you name your tele-op program "Tele-Op".
In RobotC, you can do the same thing by going to Robot->NXT Brick->Joystick Control. This is where you can pick which program to run. I know LV have a similar thing, but I don't know the details.
Here is a link where you can get help on this kind of things:
http://www.education.rec.ri.cmu.edu/.../ftc/index.htm