How do I replace them?

 

You mean the automatic transmission gear indicator light? Its a bulb....

 

Assuming you're talking about the indicator light that shows the position of your shifter, the steering wheel has to come off.

With the wheel removed, you'll see what looks like a large plastic mechanism to the left side, that's for your turn signal. On the right side is the wiring and switch mechanism for the hazards. That's actually all one big assembly containing both of those switches.
Anyway, right above the hazard switch is a 1/4 turn bulb-holder holding the light bulb you're looking for.

Easy to do, but you will need a puller to get the wheel off. A 2-leg puller will remove and OEM wheel, but if it's an after-market jobbie like a Grant wheel, you'll need a 3-leg puller for that hub.

 

This is my wheel
What kind of puller do I need.

 

This one will do it: Grant 5891 - Steering Wheel Puller | O'Reilly Auto Parts You can probably borrow one free from most auto parts stores.

The one shown will serve either a 2-bolt or 3-bolt setup.

You need to remove the horn button bar first by removing 2 screws on the back side of the wheel then get a 24mm socket to unscrew the big nut holding the wheel on. Only then will you be able to use the puller...

Edit: Try to keep the wheel turned to the straight-ahead position while undoing that big nut, it's likely to try to turn while you loosen it. Before employing the puller. I suggest you mark the exact position of the wheel relative to the column AFTER you've loosened the nut, otherwise it's possible to re-install it on the wrong spline.

 

I like the clock.

Disconnect Batt Neg cable.

Remove two screws behind horn pad, lift horn pad off, disconnect gnd wire clip, set aside.

Mark steering wheel to column so you can put it back. I actually have a small line that I scribed with a hacksaw blade across the end of the steering column shaft to show me straight ahead. A file works too.

Loosen center nut a few turns.

I never needed a puller on my '77, just sat in seat and take both open hands and slapped rear side of "fat part across center" (where horn pad was) towards me as hard as I could a few times and it popped.

Remove loose nut, pull off wheel.

But if that don't work, simple puller can be fabbed with 5/16 bolts and a bar of steel or buy one cheaply ...... they'll last a long time in a tool box.