There are several threads on the subject already so instructions should be easy to locate.
However, you don't want to order just any switch.
You preferably want:
1) a name brand part (sipea ideally)
2) the actual correct part
#1 because there is some junk out there
#2 because there was a transition from a 'short' barrel ignition switch to a 'long' barrel ignition switch around 86-87
Both switches will fit either version steering column, but the short barrel won't stick out of the clamshell on a long barrel car, and a long barrel switch will stick out too far on a short barrel clamshell.
Then there's the whole issue about whether there's a light in it or not.
Some will say the short barrels never had a light (mine does) and the long barrel has the light in all of them (many don't)
And of course, there's differences in the wiring/plugs depending on how early or late the harness on the car is around the transition and which barrel type it orginally had.