Need a simple answer about a Horn

There is usually 2 small screws that hold that button on. Haven't pulled one of those in 15 years, so memory si fuzzy.

Once you have the horn button off, you will need a steering wheel puller to remove the old wheel. The shaft that it sits on is knurled. Once you have all the wires for the horn sorted, just use a puller to extract the wheel.

I have used these kinds before:
http://www.summitracing.com/parts/GRT-5891/?rtype=10
It is setup to use either 2 or 3 bolts, so you get what you need.