I have a 1976 vette. I need to replace the key ign. switch. The problem is it is locked up . Is there anyone who knows the step by step way.

I think the chassis and service manual tells you how to do it.

You'll need to remove the steering wheel, and the hub, first. Then all of the horn contact parts. If you have the tilt/tele, you will need to remove the spring plate, then the three screws for the turn signal switch, as well as the small knob for the hazzard flashers. You do not need to remove the t-sig switch, just pull it up a bit, so you can get to the cylinder lock tab.

Once all of that is out of the way, you'll be able to see where the key cylinder ends in the column. There is a small, plastic switch there that will need to be gently pried out. This is the "key in ign" buzzer switch. There may be a small screw holding it in.
Once that is removed, you'll see a small "tab" sticking thru a slot in the column, at the end of the key cylinder. In order to remove the cylinder, that tab must be pressed down, and the cylinder pulled out while pressing the tab. There is gonna be a problem, tho, if you cannot turn the key to the "ON/Run" position, as that is the only position that will allow the tab to be pressed.

It's really not that hard of a job, but it will take a little time....and patience. If you do have the tilt/tele, you'll need the tool to re-install the spring plate. And, you'll need to fabricate a "tool" to lock the telescopic part of the column, in order to re-install the spring plate.

There are a couple of other threads here on working on the tilt/tele columns, if you would like to do a "SEARCH" on the subject. If you still need help, we're here for ya!

If you can't turn the key to the "On/Run" position and you are going to replace the cylinder anyway, can you get it out even if it means damaging the cylinder?

Thanks this will be a great help.

Why, yes...yes you can. Thanks for asking.

It is a major pain, tho, and some damage may occur. The tab is made of a fairly soft metal, which it what makes them so easy(for thieves) to run a slide-hammer in it and beat it out.
For the law-abiding citizens, you need to either use a small drill bit, and drill the tab all the way across, or, use a small grinding attachment on a drill(or die-grinder), and grind it off.
OR...you can just get heavy-handed with a hammer/chisel.

  Install a GPS Locator so that You can know the Location of the Car at all Times.  Park the Car in Newark New Jersey and or East Los Angeles. Buy the time you wake up the next Morning the job sould be done. Richard...

You can use a slide hammer but the screw has to be made of hardened steel or it will break. Screw it in as many turns as you can and dont be afraid give it a real good slam. It will come out without damage (to the car). The great part is you dont have to take anything apart. The new lock will slide right in. It is also possible to get a locksmith to rekey the new switch for you to match the old one. It is also possible to rekey yourself with parts from the old lock.