I presume you are referring to Knock Out roses, not Knock Off roses?
I don't advise cutting them down for winter. The first year you should put something on them for winter protection. It can be mulch, soil, compost, leaves, or anything else that would insulate the crown and keep the soil around it frozen.
Yes, frozen!
The idea is to prevent the soil from the freeze thaw cycles that might cause the roots to heave from the ground.
Prune in the spring to remove any dead or damaged canes and shape the bush. You can keep them cut to the size you want by deadheading with a pair of hedge shears after each bloom cycle.
When planted, you should have planted the "crown" or bud union below the soil. In your zone 4 with the cold winters you'll probably not have to worry about them getting much over three feet tall anyway.
BTW Ed, TYPING IN ALL CAPS SUGGESTS YOU ARE YELLING.

That's funny. "Knock-off." Like a freudian slip:)

Thank you for your informatiom. This is our first experiance with Knock Out Rose Bushes ( they were here when we moved in last Nov.)and I thought someone told me they were Knock Off Roses. Also sorry about the "CAPS" Thanks again for your help,Ed

Not a big deal, Ed---and we all enjoyed a little laugh over your "Knock-Offs"! If people don't stop planting those in every crevice in the ground, we're going to NEED to knock them off.

Karl, Knock Outs are knock offs, of real roses.

Carla

ooooh I love Freudian slips.

and let us not forget that sometimes a cigar is just a cigar. (wink wink)

I've always referred to them as Knock Offs, b/c to me, they ARE Knock Offs of the real thing. :) I've always wondered when people were going to catch onto that!

How about some knock off Austins at cheaper prices? Looks and smells like the real thing but costs 50% less.

Thank you everyone for your all your comments and advice. I really appreciate them. Again thanks,
Ed