You need a steering wheel puller tool to remove steering wheels easily. They cost about $15 at car parts stores. Most car parts stores will "rent" you one, but what they do around here is just collect a deposit equal to the sale price and if you never bring it back they don't care, and if you bring it back you can get a refund. I just bought mine and I'm glad I have it because I've needed it several times. You'll need it if you want to pull the steering wheel and re-center it.
Remove your steering wheel and lets see if you have a cancelling cam under there. You will need one for your GM wheel and for the horn to work. This is what they look like (from another thread)
Under that horn hardware that came with your GM wheels is the threaded holes you'll use with the steering wheel puller. It's good that your new wheels came with that hardware. Remove the 3 screws that hold the horn hardware in, and remove the items and set them aside in an orderly fashion, so you can know how to put them back in. When storing the GM wheels, I recommend putting the horn hardware back in place.
I don't know much about the Grant wheels. I think they may use an adapter of some sort, and that adapter may need to be pulled off with the steering wheel puller. Take off the horn button and see what's under there.
I recommend don't throw out the Grant wheel. Somebody will want to buy that from you, and it will probably get more than enough to pay for a premium membership here on the forum. Some people like that style of wheel.